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BIOLOGY SS 3
Theme 1: The Organism at Work
Theme 2 The Organism And Its Environment
Theme 3 Continuity of Life
Homeostasis refers to the process by which organisms maintain a relatively stable internal environment. The internal environment comprises body fluids such as blood, lymph, and tissue fluid. In order for body cells to function optimally and for healthy growth, living organisms must be able to adapt to changes in the physical and chemical conditions of their body fluids. These conditions include temperature, pH, osmotic pressure, concentrations of dissolved substances, and mineral ions.
Homeostatic processes involve control mechanisms that detect and respond to changes in the organism’s internal environment. These mechanisms typically include:
In unicellular organisms, osmoregulation (homeostasis) is ensured by the use of a contractile vacuole. In multicellular organisms, various organs contribute to homeostasis, including the kidney, liver, skin, ductless glands (hormones), and the brain, which has overall control of the homeostatic process in the body.
The mammalian kidney is a reddish-brown, bean-shaped organ located in the posterior end of the abdomen. The right kidney is slightly lower than the left. On cutting a kidney longitudinally, two distinct regions are observed: an outer cortex and an inner medulla. Narrow tubules called urinary tubules (nephrons) pass through these two regions. The tubules open at the tips of triangular-shaped masses of tissues called pyramids, which in turn open into a funnel-shaped cavity called the pelvis. The kidney has many tiny capillaries, which are branches of the renal artery and renal vein. The pelvis continues as the ureter, a long narrow tube connecting the kidney to the urinary bladder.
The kidney serves as the chief osmoregulator and excretory organ in mammals, performing the following functions:
The first three functions are related to excretion, while the last three are osmoregulatory functions of the kidney.
The kidney acts as an osmoregulator by maintaining the water, salt, and pH balance of the blood, primarily in the distal tubules and collecting ducts of the urinary tubules.
When the body is dehydrated, the osmotic pressure of the blood increases. Osmoreceptors in the hypothalamus detect these changes and stimulate the pituitary gland to secrete more antidiuretic hormone (ADH). ADH makes the walls of the urinary tubules more permeable, leading to increased water reabsorption into the blood. This results in less water being lost from the body, and concentrated urine is produced.
When the body is hydrated, the osmotic pressure of the blood is lowered, resulting in the secretion of less ADH. Consequently, the walls of the kidney become less permeable, and more water is lost from the body as dilute urine.
The concentration of sodium ions in the blood is regulated by excreting the excess or reabsorbing more, which is controlled by the hormone aldosterone.
The blood pH of 7.4 is maintained by excreting hydrogen ions when the pH becomes acidic and excreting hydrogen carbonate ions when it becomes alkaline.
KIDNEY DISEASES
EFFECTS OF KIDNEY DISEASES
REMEDIES
There are five groups of animal hormones secreted by different glands.
The pituitary gland is located below the hypothalamus and consists of anterior and posterior parts. The anterior pituitary gland releases growth hormones and tropic hormones that regulate other endocrine glands. It is often referred to as the “master gland.” The hormones secreted by the anterior pituitary include:
The posterior pituitary gland secretes:
The thyroid gland, located in the neck region close to the larynx, produces three main hormones: thyroxine, triiodothyronine, and calcitonin.
The primary hormone is thyroxine.
Thyroxine:
The parathyroid glands, which are small glands attached to the thyroid gland, secrete a hormone called parathyroid hormone (PTH). PTH plays a crucial role in regulating blood calcium levels. It achieves this by:
The hormone calcitonin, produced by the thyroid gland, has the opposite effect and lowers blood calcium levels. Over secretion of parathyroid hormone leads to fragile bones prone to fractures, while under secretion causes muscle spasms.
The pancreas serves both as a digestive gland and an endocrine gland. It contains specialized cells called Islets of Langerhans, which produce two important hormones: insulin and glucagon.
Insulin lowers blood glucose levels by stimulating liver cells to convert excess glucose into glycogen for storage in the liver and muscles. Deficiency of insulin leads to diabetes mellitus, characterized by glucose excretion in urine, reduced appetite, and increased thirst. Excessive secretion of insulin causes a drop in blood sugar levels and constant hunger.
Glucagon, on the other hand, raises blood glucose levels by stimulating the liver to convert stored glycogen into glucose.
The adrenal glands, located above the kidneys, produce two distinct groups of hormones. The adrenal cortex produces corticosteroids, while the adrenal medulla produces adrenaline and noradrenaline, known as emergency hormones.
Corticosteroids include glucocorticoids, such as cortisol, which raise blood glucose levels during times of stress, and mineralocorticoids, such as aldosterone, which regulate sodium and potassium ion levels in body fluids.
Adrenaline, as an emergency hormone, prepares the body for immediate action in response to fear, danger, or anger. It achieves this by:
Under-secretion of adrenaline results in a slow response to emergencies, low blood pressure, and heart rate, while over-secretion leads to excessive anxiety and excitement.
Reproductive hormones are produced by specific cells in the reproductive organs. In males, the testes produce testosterone, the male sex hormone, while in females, the ovaries produce estrogen and progesterone, the female sex hormones.
Testosterone stimulates:
Estrogen performs the following functions in females:
Progesterone:
Excessive secretion of reproductive hormones leads to excessive development of sexual organs and abnormal sexual urges, while under secretion results in poor development of secondary sexual characteristics, sexual organs, and decreased sexual drive.
Plant coordination relies on chemicals known as plant hormones. These hormones share similarities with animal hormones in that they:
However, plant hormones differ in that they are not produced exclusively in specialized glands but have more generalized effects based on concentration and organ type. Plant hormones regulate growth, fruit formation, root development, leaf fall, and other activities. Combinations of plant hormones can result in unique responses beyond what each hormone can accomplish alone. Although slower than animal hormones, plant hormone responses mainly occur through growth processes.
The major groups of plant hormones include auxins, gibberellins, cytokinins, abscisic acid, and ethylene.
The primary naturally occurring auxin is indoleacetic acid (IAA), produced at the shoot apex. It influences cell division, elongation, and differentiation. Auxin:
Gibberellins are found in root and stem apices. They promote growth by stimulating both cell elongation and division. They are also effective in promoting growth in dwarf plant varieties. Other effects of gibberellins include inducing seed germination and increasing fruit size.
Cytokinins are produced in roots and promote growth, similar to auxins and gibberellins. They stimulate cell division, ensuring normal stem and root growth. Unlike auxins, cytokinins stimulate lateral buds to grow into branches and delay aging in plants.
Produced in mature green leaves, fruits, and root caps, abscisic acid acts as a growth inhibitor that generally opposes the effects of auxins and gibberellins. It:
The effects of abscisic acid help plants withstand adverse environmental conditions.
Ethylene, a simple hydrocarbon, is produced in leaves, stems, and young fruits. It inhibits lateral bud development and accelerates fruit ripening.
Both natural and synthetic plant hormones find applications in horticulture and agriculture. Some common uses include:
SENSORY RECEPTORS
Living organisms have the ability to respond to changes in their environment, known as stimuli. These stimuli can be of various types, including mechanical, electromagnetic, chemical, or thermal. While most cells in an organism’s body are capable of sensing stimuli, certain cells specialize in detecting specific types of stimuli. These specialized cells are called sensory receptors or sense cells, and they are abundant in the human body, constantly monitoring the internal environment.
Mechanoreceptors are sensory receptors that respond to mechanical changes, while thermoreceptors, chemoreceptors, and photoreceptors are sensitive to heat, chemical substances, and light, respectively.
Sensory receptors convert the detected stimuli into electrical impulses, which are then transmitted to the brain. The brain interprets these impulses, translating them into visual images, sounds, smells, or taste sensations. Structures that contain sensory receptors are referred to as sense organs.
A sense organ is defined as a group of specialized cells or tissues that can receive, perceive, or detect stimuli and transmit the information to the central nervous system. In mammals, there are five types of sense organs:
The mammalian skin contains numerous sensory receptors that detect various stimuli such as touch, pressure, pain, cold, and heat. Unlike other sense organs, which specialize in detecting a single type of stimulus, the skin’s sensory receptors are capable of responding to multiple stimuli.
Sensory receptors are not evenly distributed throughout the skin. Each type of receptor is concentrated in specific regions of the body. Receptors sensitive to pressure, known as Pacinian corpuscles, are found deep within the skin and require stronger stimulation. Receptors sensitive to touch, called Meissner’s corpuscles, are predominantly distributed close to the surface of the skin, especially in hairless regions like the tongue, fingers, lips, and forehead. These receptors respond to gentle stimulation. Between the pressure and touch receptors, there are receptors that detect cold, heat, and pain.
The eye is the organ responsible for vision. It has a spherical shape and is protected by ocular or optical structures such as eye sockets, eyelids, eyelashes, tear or lacrimal glands, and conjunctiva.
The wall of the eyeball consists of three layers, from the outermost to the innermost: sclera, choroid, and retina.
2. THE CHOROID LAYER: This highly vascularized and pigmented layer (black) supplies nutrients and oxygen to the eye’s cells. The black pigment helps absorb light rays and prevents light reflection. The choroid layer includes the ciliary muscles, iris, pupils, suspensory ligaments, and the lens.
3. THE RETINA: This part of the eye is sensitive to light. It is also vascularized, pigmented, and elastic. Light rays converge on the retina, forming images that are real, inverted, and smaller than the actual objects. The retina contains two types of sensory cells called cones and rods.
The eye performs two major functions: image formation and accommodation.
Light rays from an object enter the eye through the cornea, pass through the aqueous humor, lens, and vitreous humor, and finally reach the retina. These transparent structures refract (bend) the light rays, allowing them to converge on the retina. As a result, an image of the object is formed on the retina, appearing real, inverted, and smaller than the actual object. The light stimulus reflected from the object is received by the cones or rods, depending on the light intensity. These sensory cells convert the stimulus into electrical impulses, which are then transmitted through the optic nerve to the optic lobe of the brain. The
brain accurately interprets the image. To create a sharp image on the retina, all the refracted light rays must meet at a specific point on the retina known as the yellow spot.
This refers to the eye’s ability to focus on objects at different distances, enabling clear vision. Accommodation involves adjusting the focal length of the lens to focus near and distant objects onto the retina.
Eye defects occur when an image cannot be properly formed on the retina. Some common eye defects include:
Short-sightedness (myopia):
Long-sightedness (hypermetropia):
Presbyopia:
Astigmatism:
Cataract:
Night blindness:
Conjunctivitis:
Mammals possess a bilateral auditory system consisting of two ears located on each side of the head. The majority of the auditory system is protected within the skull. Its primary functions are hearing and maintaining balance.
The mammalian ear can be divided into three main parts: the outer ear, the middle ear, and the inner ear.
The outer ear comprises the following structures, starting from the outside of the organism:
The middle ear is a small air-filled chamber within the skull. It consists of three tiny bones called ear ossicles (malleus, incus, and stapes) and the Eustachian tube.
The inner ear consists of a complex bony structure known as the bony labyrinth, filled with perilymph fluid. Within the bony labyrinth, there are membranous sacs and tubes called the membranous labyrinth, which are filled with endolymph fluid. The cochlea and the semicircular canals are the two auditory structures connected to the utriculus and sacculus, respectively.
The ear performs two major functions: hearing and balancing.
Mechanism of Hearing:
The pinna collects and focuses sound waves, which then pass through the external auditory meatus. The sound waves cause the eardrum to vibrate, and these vibrations are transmitted to the ear ossicles, which amplify them. The oval window further magnifies the vibrations, sending them into the inner ear (cochlea) where the perilymph and endolymph fluids vibrate. These vibrations stimulate the organ of Corti within the cochlea, which converts sound vibrations into electrical impulses. The impulses then travel through the auditory nerves to the brain for interpretation.
Mechanism of Balancing:
Movement of the head in any direction causes the fluid within the semicircular canals and the otoliths in the ampullae to move. This movement generates impulses that travel through the vestibular branch of the auditory nerves to the brain for interpretation. The brain then relays impulses to the body’s muscles to maintain balance and body position.
Deafness is the primary disorder associated with the ear. It can be temporary or permanent and may result from various causes, including damage to the eardrum, Eustachian tube, or sensory cells in the cochlea. Factors such as wax blockage, ear infections, or exposure to loud noises can also lead to deafness.
To maintain ear health, it is important to follow these guidelines:
The nose serves as the olfactory organ in humans. The epithelial lining of the nasal cavity contains sensory nerve endings. Although humans have a relatively poor sense of smell compared to some animals like dogs, we can quickly detect smells, albeit for a limited duration.
The nose functions optimally when moist. Smell receptors within the nasal cavity are stimulated by chemical substances. Volatile particles in the air dissolve in the mucus layer covering the receptor cells in the nostrils. Stimulation of these receptors generates nerve impulses that travel through the olfactory nerve to the olfactory lobe of the brain. The brain then interprets the type of smell detected.
Taste buds, which are sensory cells, are responsible for detecting taste. These taste buds are located on small protrusions on the tongue’s exposed surface. Four sensory nerves connect the taste buds to the brain, enabling the interpretation of taste sensations. The tongue is sensitive to four primary tastes:
When substances are placed in the mouth, chemicals dissolve in the saliva on the tongue’s surface. This dissolution stimulates the sensory nerve endings within the taste buds, which then transmit impulses to the brain for interpretation as sweet, bitter, sour, or salty tastes.
NOTE: Smell and taste are closely related sensations, and we often experience them together. When we eat or drink, taste receptors are stimulated, and simultaneously, flavor-producing chemicals dissolve in the moist air within the mouth and flow into the nasal cavity, stimulating smell receptors. The sensation of smell is often more pronounced than that of taste.
GENERAL EVALUATION
1. Advantages of Having Two Ears:
Having two ears provides several benefits, including improved sound localization and a more accurate perception of sound intensity. It also aids in better speech comprehension and enhances the ability to differentiate between different sound frequencies.
2. Types of Deafness:
There are two main types of deafness:
3. Mechanism of Smelling:
Smelling involves the stimulation of smell receptors in the nasal cavity by volatile chemical substances. These receptors generate nerve impulses that are transmitted to the olfactory lobe of the brain for interpretation.
4. Functions of the Organ of Smell:
The organ of smell serves the following functions:
An ecological population refers to a group of individuals of the same species that live in the same area and interact with each other. This concept is fundamental to the field of ecology, which is the study of how organisms interact with each other and their environment. A population is defined by its specific geographic location, its members’ ability to interbreed, and its potential to increase in number through reproduction.
Succession is a process of ecological change in a specific area over time. It describes how the composition of species and the structure of an ecosystem evolve and change as an area transitions from a barren or disturbed state to a more mature and stable state. Succession can be classified into two main types: primary succession, which occurs in areas without any previous biological community, and secondary succession, which happens in areas that have been previously colonized by life but have been disturbed or disrupted.
This phrase describes the changes that occur in an ecosystem as it progresses through succession. Initially, in a barren or disturbed area, there may be only a few species present. As succession occurs, new species arrive, biodiversity increases, and the overall structure of the ecosystem becomes more complex. This is often accompanied by an increase in the population numbers of various species as the ecosystem becomes more stable and provides more resources.
Primary succession in an aquatic habitat involves the colonization and establishment of life in a water body that previously lacked any significant biological community. This can happen, for example, in newly formed ponds or lakes created by geological processes such as glacial retreat. Over time, aquatic plants, algae, and animals gradually colonize and establish themselves, leading to a more complex and stable aquatic ecosystem.
This type of succession initiates from barren land, exposed rock surfaces, or unoccupied bodies of water.
The process of primary succession on land can be observed in scenarios like a construction site where a pile of subsoil, rocks, or concrete blocks remains after building. In aquatic environments, primary succession can be witnessed in newly formed artificial ponds.
The pioneers of any succession, referred to as primary colonizers, are typically autotrophic plants. These plants have uncomplicated life requirements and can endure harsh conditions. As the primary succession progresses into its second year, the growth of algae, lichens, and mosses may become more pronounced. Over time, these organisms contribute to soil formation through growth, decay, and decomposition.
Moving into the third year, small herbaceous plants might establish themselves. These plants play a role in transforming the habitat by outcompeting smaller plants, leading to their decline. The dropping of leaves from these plants further contributes to soil enrichment, making it more conducive for other organisms. As years pass, an increasing variety of species join the habitat, while some species dwindle. This succession of species continues until a climax community is achieved. This climax community heralds the presence of larger life forms like shrubs and trees.
Secondary succession refers to the ecological process that occurs in an area that has previously supported life but has been disturbed or disrupted by events such as fires, clear-cutting, or abandoned agricultural land. The existing soil and some plant and animal species still remain, allowing for a faster and somewhat different recovery process compared to primary succession. An example would be a forest regrowing after a wildfire.
Secondary succession takes place in areas where soil and vegetation haven’t been completely eradicated. This process unfolds at a faster pace compared to primary succession, owing to the pre-existing presence of soil. Additionally, it transpires when a farmer abandons an old field. The commencement of secondary succession stems from a pre-established community that has experienced disturbances due to human activities and other influencing factors. Incidents such as fire, drought, and floods can trigger secondary succession.
| PRIMARY SUCCESSION | SECONDARY SUCCESSION | |
| 1 | Starts on a bare surface | Starts on already colonized surface |
| 2 | It is slower or takes longer time to reach a climax community | It is faster or takes a shorter time to reach a climax community |
| 3 | Starts with lower organisms | Starts with fairly complex organisms |
Competition plays a significant role in the process of succession. As species colonize an area, they often compete for resources like sunlight, water, and nutrients. Over time, certain species that are better adapted to the available resources become dominant, leading to changes in the composition of the ecosystem. Succession involves a gradual shift from early colonizers, which are usually r-strategists and opportunistic species, to later successional species that are often K-strategists and more specialized.
Overcrowding in a population can result from factors such as limited resources (food, water, shelter), high birth rates, low death rates, and reduced emigration. When a population exceeds the carrying capacity of its environment, it can lead to competition for resources and stress on the ecosystem.
Populations can avoid overcrowding by various means, including controlling birth rates through reproductive strategies, dispersing to new areas through emigration, and adapting behaviours to manage resource utilization. Predation, disease, and other ecological factors also play a role in naturally regulating populations.
Food shortage can have several effects on a population. Competition for limited food resources can increase as organisms strive to secure enough sustenance to survive and reproduce. This competition can influence reproductive rates, with some individuals potentially reproducing less if resources are scarce. Additionally, in response to food scarcity, the emigration rate might increase as individuals seek out areas with better resource availability. Overall, food availability can significantly impact population dynamics and ecosystem interactions.
In the realm of nature, a state of dynamic equilibrium prevails. When environmental conditions influenced by population dynamics, encompassing both abiotic and biotic elements, are propitious, growth is encouraged. Conversely, when these conditions turn unfavorable, growth is hindered. A constraining element that curbs population expansion is termed a “limiting factor.” The amalgamation of all these constraining factors constitutes what is termed as “environmental resistance.”
The interplay between abiotic and biotic factors culminates in a state where the population size of organisms strives for a dynamic equilibrium, colloquially referred to as the “balance in nature.” As the population swells, so does the force of environmental resistance. A pertinent example is the depletion of food resources within a population, instigating a competitive struggle that ultimately leads to the demise of the weaker organisms. This cyclical process serves to maintain the population at a relatively steady level.
The term “population” alludes to the collective count of organisms belonging to the same species, coexisting within a designated area at a specific juncture. Within an ecosystem, the conglomeration comprises diverse species’ populations, forging a multifaceted biotic community. When these assorted populations within an established ecosystem display sustained equilibrium, the community attains a state of balance.
The multiplex factors that govern the populace of organisms in a particular habitat collectively constitute “environmental resistance.” These factors are broadly classified into two categories:
These encompass components such as heat, water, space, light, and nutrients.
These factors comprise the actions and interactions of organisms that reverberate upon one another. They encompass a spectrum of dynamics, including food availability, competition, natality, mortality, dispersal, parasites, predators, and pathogens.
Within the natural world, a biological equilibrium manifests through the dynamic of predator and prey. In the realm of human beings, a parallel equilibrium is established through the practices of family planning and birth control. Family planning constitutes a mechanism through which couples ascertain the desired number of offspring and the timing of their arrival.
Birth control, on the other hand, encompasses techniques utilized to prevent a woman from conceiving for the duration she desires.
In the absence of effective family planning, a nation’s population could escalate without restraint, potentially outstripping the capacity of accessible nourishment and resources. This scenario could culminate in famine and loss of life.
Family planning is dedicated to averting pregnancies rather than terminating existing life. Meticulously devised family planning strategies serve to thwart unplanned pregnancies. The arsenal of birth control and family planning methods encompasses:
Each testis consists of numerous coiled tubes known as seminiferous tubules. Enclosed within a scrotal sac suspended between the thighs, this positioning ensures that sperm are maintained at a lower temperature than that of the body.
The lining of the seminiferous tubules comprises actively dividing cells that give rise to sperm. Interspersed among the seminiferous tubules are interstitial cells responsible for producing male hormones such as androgens (e.g., testosterone). These tubules combine to form the epididymis, a coiled tube that temporarily stores sperm.
The vas deferens is the conduit through which sperm travel from the testes to the urethra.
The seminal vesicle produces an alkaline secretion that nourishes the spermatozoa.
The prostate gland produces an alkaline secretion aimed at neutralizing vaginal fluids.
The bulbourethral gland secretes an alkaline fluid. Together with spermatozoa, these fluids constitute semen.
The urethra is a lengthy tube responsible for conducting semen during copulation. It also facilitates the removal of urine from the bladder.
The penis is an intromittent organ used for insertion into the vagina during copulation.
Fertilization in animals is a pivotal reproductive process. It follows copulation, during which the erect penis is inserted into the vagina, leading to the release of semen. Within the female’s genital tract, sperms traverse to the upper region of the oviduct.
The sperm’s head penetrates the egg after the acrosome releases lytic enzymes, dissolving the egg membrane. The tail of the sperm is left behind. Subsequently, the sperm nucleus merges with the ovum’s nucleus, resulting in the formation of a zygote.
A fertilization membrane envelops the zygote, effectively preventing other sperms from entering it.
Following fertilization, the zygote begins mitotic division while moving towards the uterus. It becomes embedded within the uterine wall, a process termed implantation. At this stage, the zygote takes on the form of a hollow cell cluster referred to as a blastocyst or embryo.
In the uterus, the embryo develops villi that extend into the uterus, serving as a source of nourishment. Over time, these villi and the endometrium transform into the placenta.
Membranes that envelop the embryo start to develop. The outermost membrane, the chorion, forms finger-like projections known as chorionic villi, which nourish the embryo. The amnion encloses the embryo, creating a fluid-filled cavity where the embryo resides. This fluid acts as a protective cushion, guarding the fetus against physical harm and temperature fluctuations. The placenta is formed by the chorionic villi, allantois, and endometrium working in concert. The embryo connects to the placenta through the umbilical cord, housing both umbilical vein and artery.
Maternal and fetal blood circulation remains separate, preventing harmful pathogens and toxins from reaching the fetus. The placenta, however, allows maternal antibodies to pass into the fetus, enhancing its immunity.
The placenta facilitates the transfer of nutrients from the maternal bloodstream to the fetus.
Nitrogenous waste removal from the fetal blood to the maternal blood is facilitated by the placenta.
Oxygen from the maternal blood moves into the fetal blood through diffusion, while fetal carbon dioxide diffuses into the maternal blood.
The placenta produces hormones like progesterone and estrogen.
Fertilization initiates a series of intricate processes that culminate in the formation of the zygote, its implantation, and the development of crucial structures like the placenta. The placenta serves as a multifunctional interface between the maternal and fetal systems, providing protection, nutrition, waste removal, gaseous exchange, and hormone production for the developing fetus.
It seems like you’ve provided two points, but they might be related to a broader context. From the phrasing, it appears that you might be discussing physiological processes that occur during pregnancy. Let’s break down each point:
During pregnancy, the mother’s body and the developing fetus establish a connection through the placenta. The placenta is a temporary organ that develops in the uterus and serves as a means of exchanging nutrients, oxygen, waste products, and other substances between the mother’s blood and the fetus’s blood.
This process involves a selective exchange of molecules. Nutrients, such as glucose, amino acids, vitamins, and minerals, are transported from the mother’s blood to the fetus’s blood to support its growth and development. Oxygen is also transferred from the mother’s blood to the fetus’s blood, ensuring that the fetus receives the oxygen it needs for respiration.
Conversely, waste products like carbon dioxide and metabolic waste are transported from the fetus’s blood to the mother’s blood, where the mother’s body can eliminate them. This exchange is crucial for maintaining a healthy environment for both the mother and the developing fetus.
As the fetus develops, it produces waste products from its metabolic processes, just like any living organism. These waste products include carbon dioxide, which is a byproduct of cellular respiration, and other metabolic waste substances.
The placenta, as mentioned earlier, facilitates the removal of these waste products from the fetus’s blood into the mother’s blood. Once in the mother’s blood, these waste products are transported to the mother’s organs, such as the lungs for carbon dioxide removal and the kidneys for processing other waste materials. The mother’s body then eliminates these waste products through processes like breathing and urination.
These two points are related to the physiological processes that allow the mother and developing fetus to share necessary substances while ensuring the removal of waste products. This exchange is facilitated by the placenta, a unique structure that develops during pregnancy to connect the maternal and fetal circulatory systems.
In flowering plants, the process of pollination is followed by fertilization, leading to the development of the zygote. This development eventually transforms the flower into a fruit that encloses the seeds. The male and female sex cells responsible for zygote formation are the pollen grain and the ovule, respectively. The following steps outline the processes involved:
The zygote undergoes division through mitosis, forming multiple cells that differentiate and organize into an embryo. The embryo consists of the following parts:
As the embryo develops, the ovary and ovules undergo changes and develop into fruits and seeds, respectively.
A seed is the ripened, fertilized, and developed ovule. It comprises the following parts:
Seeds with a single seed leaf are known as monocotyledons, such as maize, millet, rice, sorghum, and wheat. Seeds with two seed leaves are called dicotyledons, such as mango and beans.
Germination is the gradual development of the seed embryo into a seedling or young plant. Embryos of developed seeds often undergo a period of rest called dormancy until favorable conditions for germination arise. There are two types of germination:
For seeds to germinate successfully, the following conditions are required:
A fruit is a matured fertilized ovary of a flower containing one or more seeds. Contrary to this, some plants do not undergo fertilization for the formation of their fruit. Such fruits are called parthenocarpic fruits e.g. banana and pineapple. Such fruits are seedless.
A typical fruit has the following parts
Fruits are classified based on their origin or structure. Common ways of classifying fruits are
True and false fruit:
A true fruit develops from a fertilized ovary and contains a pericarp and seed(s) e. g. mango, and cowpea while a false fruit develops from the ovary and other floral parts e. g. apple, and cashew.
Simple, aggregate and composite fruits
A simple fruit develops from a single flower with a single ovary e. g. cowpea, maize. An aggregate fruit develops from a single flower with several ovaries (each ovary develops into a fruitlet to form a cluster). The fruits have a common fruit stalk e. g. custard apple and strawberry. A composite fruit develops from an inflorescence e. g. fig, breadfruit.
Fleshy and dry fruits
Fleshy fruit is a fruit that has the whole pericarp or at least one of the pericarp thick, soft and succulent is a fleshy fruit. There are six types of fleshy fruits:
Dry fruit is a type of fruit in which the pericarp becomes dry, hard, woody or fibrous when the fruit ripens. Dry fruits can be grouped into dehiscent or indehiscent fruits
Dehiscent fruits split open to release the seeds when ripe. Four main types are
Indehiscent fruits fall to the ground when ripe, eventually decayed to release the seeds. Five main types are
This is the transfer of the seed or fruit from the parent plant to other places where such seed may germinate. The essence of dispersal includes the following:
These are the means by which seeds and fruits are removed from parents to other places. These agents include:
Features that aid methods of dispersal
Courtship behavior in animals refers to a set of behaviors and displays that individuals of a species engage in to attract potential mates and establish a reproductive partnership. This behavior often involves various signals, sounds, postures, and movements that communicate the fitness and availability of an individual for mating. Courtship behaviors help animals recognize compatible partners and reduce the chances of mating with individuals from other species or those not ready for reproduction.
Territoriality, on the other hand, refers to the behavior exhibited by animals to establish and defend a particular area or territory. Territorial animals mark their territory with various cues, such as scent markings or vocalizations, to signal ownership and deter other members of the same species from entering. In the context of courtship, territoriality can play a role by allowing animals to secure a suitable area for mating and raising offspring. Displaying ownership of a territory can also be an attractive trait for potential mates, as it demonstrates the ability to provide resources and protection.
Many animals use vibrant colors and distinctive body parts to communicate with each other and their environment. These displays serve various purposes, including courtship, warning predators, and establishing social hierarchy. The colors and body parts may be used to attract mates, signal readiness to mate, or indicate dominance within a group.
For example, in birds, males often have bright and colorful plumage that they display during courtship rituals to attract females. Peacocks are a classic example of this; their elaborate tail feathers are used in courtship displays. Similarly, some fish species change colors or patterns during breeding seasons to signal their readiness to mate. Insects, like butterflies, also use vibrant wing patterns to signal their presence to potential mates and to ward off predators.
Seasonal migration is a phenomenon where animals move from one location to another in response to changing environmental conditions, usually related to factors like food availability, climate, or reproduction. This behaviour helps animals find better resources, and suitable breeding grounds, or escape unfavourable conditions.
Mutual flight, as seen in termites, refers to a synchronized mass movement of winged termites during their reproductive phase. Winged termites, known as alates, emerge in large numbers from their colonies and engage in flight to find new mates and establish new colonies. This phenomenon often occurs during specific times of the year, and the termites are drawn to light sources as they fly. Once they find a suitable partner, they shed their wings and start the process of creating a new termite colony.
These behaviours are all fascinating examples of how animals adapt and communicate in order to ensure successful reproduction, secure resources, and thrive in their environments.
10.A Locus denotes the gene’s location on a chromosome.
Hereditary variation denotes differences among individuals transmitted from parents to offspring, except in identical twins. It arises due to:
Transmittable characters in animals encompass physical traits (e.g., body stature, skin color), genetic conditions (e.g., sickle cell anemia), and sensory abilities (e.g., taste).
Transmittable characters in plants include traits related to growth, fruit, leaf, color, disease resistance, and more.
Transmission of characters occurs through genes. Diploid organisms produce haploid gametes through meiosis. Upon fertilization, gametes fuse into diploid zygotes, each containing two gene copies.
Hence, characters determined by genes are transmitted from parents to offspring through gamete
In the study of genetics, Gregor Mendel (1866) worked with the garden pea
(Pisumsativum) because of three unique properties present in it. These are
The Mendel’s methods of studying genetics are two:
Mendel crossed two different plants which differ in one pair of contrasting characters e.g. tall and short plants. The procedures he followed are as follows:
This experiment resulted into Mendel’s first law of inheritance which is based on the principle of complete dominance.
Mendel’s first law of inheritance otherwise known as the law of segregation of genes states that paired alleles segregate from each other when the homologous chromosomes on which they reside separate during meiosis. Each gamete receives one of the two alleles. The actual segregation occurs in F2 generation.
Gregor Mendel crossed plants which differ in two pairs of contrasting characteristics e.g seed shape (round or wrinkled seeds) and seed colour (yellow or green seeds). He crossed plants having round and yellow seeds with these having wrinkled and green seeds. The F1 seeds were having round and yellow seeds. Self-pollinating F1 plants produced the F2 plants of four (4) types
This experiment resulted into Mendel’s second law of inheritance
Mendel’s second law of inheritance otherwise known as law of independent assortment of genes state that alleles of genes on different chromosomes assort independently during meiosis
A dominant phenotype has the genotypic patterns RR, Rr. The genotype is determined using test cross or back cross
Test cross is the crossing of an organisms with an homologous recessive organism
Back cross is the crossing of an organism with an homologous recessive organism from the original parental generation
This deal with the ability of two contrasting alleles to interact and produce a heterozygous phenotype that is different from the two homologous phenotypes: Examples of organisms exhibiting incomplete dominance include: Mirabilisjalapa,4 o’clock plant, Audlausian fowl. This principle opposes Mendel’s principle of complete dominance.
CO – DOMINANCE
In co-dominance, both alleles in the heterozygous individuals are fully expressed. The effect of one is not modified by the presence of the other. Therefore, three distinct phenotypes are produced e.g Inheritance of human “ABO” blood group
Allele 1A implies the addition of antigen A to the cell surfaces of red blood cells resulting in a person with group A blood. Likewise Allele 1B implies the addition of antigen B to the cell surfaces of red blood cells resulting in a person with Group B.
In a heterozygous individual, (1A 1B) both antigens A and B are added to the cell surfaces of red blood cells. So the individual has blood group AB.
NOTE: 1A and 1B are co-dominants while 1Ois recessive.
Multiple alleles
Genes that have more than two alleles in the population are said to have multiple alleles e.g. the human ‘ABO’ blood grouping
Each body cell of human beings has 23 pairs (46) of chromosomes, 22 of which are autosomes and a pair is sex chromosome. In male the two sex chromosomes in each body cell are X and Y chromosomes, therefore, each male gamete carries either X or Y chromosome. In the female, all egg cells of the body contain two X chromosomes. Therefore all egg cells contain one X chromosomes each. At fertilization, the combinations of an egg with a sperm carrying either X or Y chromosome occurs by chance. The formation of a male or female offspring has equal chances as shown below parents:
Chromatin granules (thread – like structures) found in the nucleus of eucaryotic cells are the precursors or raw materials of chromosomes.
Chromosomes occur in pairs known as homologous chromosomes. Each chromosome is made up of two threads called chromatids joined at a point called centromere. Each human somatic cell has 46 chromosomes. These are present in 23 pairs of homologous chromosomes. The number of chromosomes in each somatic cell of an organism is called diploid number (2n).
Each chromosome is made up of protein units in a strand of deoxyribonucleic acid, DNA (in double helix). Along its length are genes arranged which are actually DNA segments. The DNA is a very large molecule made up of repeating units called nucleotides. Each nucleotide is made up of deoxyribose (a sugar molecule), phosphate and an organic nitrogenous base which may be adenine, guanine, thymine or cytosine. Guanine always pairs with cytosine and adenine with thymine. The two helical chains are referred to as complementary strands of DNA since one is the exact opposite of the other.
There are forty-four autosomes which are similar in shape and size in both male and female. The last pair is called sex chromosome which are of genotype XX in female and XY in male. Exception to this is in birds, moths and butterfly where the female has genotype XY and the male XX. Also, in certain grasshoppers, the Y chromosome is absent so that the male has the genotype XO.
Just before cell division, the protein bundles come together and the DNA strands coil tightly around them, causing the chains to shorten and become visible under the light microscope. This process is called condensation
Each DNA molecule is made up of thousands of genes. The DNA molecules coil around the 23 pairs of chromosomes. In human body cells are about 50,000 genes. Each DNA molecule can make an exact copy of itself in a process called replication. This forms the basis for the transmission of hereditary materials from parents to the offspring.
Genes are the expression of hereditary characters in organisms and are located on the chromosomes of a body cells. Therefore chromosomes are responsible for the transmission of characters from parents to offspring. Chromosomes are arranged in pairs known as homologous chromosomes (exactly alike in shape and size and carry genes responsible for the transmission of the same characteristics). The genes relating to the same character e. g. tallness and shortness occupy identical loci on the homologous pair. The genes on homologous pair of chromosomes determine whether the individual will be homozygous or heterozygous for certain characters.
Sex–linked traits are characteristics whose genes are carried on the X chromosome of the sex chromosomes instead of autosomes. Such genes are inherited along with such X chromosomes. They are all controlled by a recessive gene. Examples of Sex-linked traits are: colour blindness, haemophilia, baldness, sickle cell anaemia and albinism.
Probability is usually expressed in units ranging from 0 – 1. Mendel’s works were based on probability.
Mathematically,
Probability = No of times an event occurs
Total no of trials
The two guiding principles of probability in genetics are:
In agriculture
Genetics is relevant and has led to the following:
In medicine
Genetics helps in the following:
NOTE: All the applications listed above sum up the relevance of biology to life in what is now termed biotechnology. In biotechnology the DNA is now being manipulated to the benefits of humanity i.e. genetic engineering
Population is a group of organisms of the same specie living in a specified area within a given period of time. Variation refers to the differences which exist between individuals of the same species
Morphological variation is the noticeable physical appearance of individuals of the same species. This physical appearances change gradually within a population. The feature observed shows a gradual transition between two extreme forms (continuous variation) e.g. size (height or weight), colour and finger prints.
Physiological variation is the difference in the ways individuals of the same species behave or react to conditions in their environment. It is not visibly apparent like morphological variation. It relates to the functioning of the body. In physiological variation, organisms can be grouped into two or more classes within a population without any graduation or intermediate between or among them (discontinuous variation). Examples of such variation are behaviour which can be temperamental, accommodating, excited or calm, blood groups, ability to roll the tongue, ability to taste phenylthiocarbamide etc.
There are two causes. They include:
Genetic differences
A sudden change in a gene called mutation can be inherited when sex linked. This then brings about variation e.g. a gene responsible for green fruits in plants may be altered to produce a yellow fruit in the same plant
Environmental differences
Environmentinclude housing, food, healthcare, educational facilities, parental care etc. e.g. an intelligent person exposed to an unfavourable environment becomes dull.
| DONOR
RECIPIENT |
A
(Antigen a) |
B
(Antigen b) |
AB
(Antigen a + b) |
O
(None) |
| A (Antibody b) | + | – | – | + |
| B (Antibody a | – | + | – | + |
| AB (None) | + | + | + | + |
| O (Antibody a + b) | – | – | – | + |
+ means positive reaction (no clumping)
Note: O is a universal donor while AB is a universal recipient
Competition is the process by which living organisms in the habitat struggle with one another for limited essential needs in the environment. Such scarce resources in plants include; light, space, nutrient and water while animals complete for food, space or mate.
Competition finally results in survival of the fittest and elimination of the unfit.
Intraspecies competition: competition between organisms of the same species. e.g. many maize seedlings grown in a small area.
Interspecies competition: that between different species of organisms. e.g. many maize and pepper seedlings growing in a small area.
Relationship between competition and succession
Succession is the change in a population caused by the replacement of the old members with new ones as a result of competition. The newly formed habitat is gradually colonized by different species of plants in a stepwise manner until a relatively stable community is established and later the habitat will be inhabited by animals. As soon as a habitat is established, competition sets in. The early inhabitant modify the habitat by their activities while the later arrivals compete and outgrow the previous inhabitants which gradually loss out.
Adaptation is the possession of special features which improve the chances of an organism to survive in its environment. All organisms have adaptive structures which could be structural or morphological and behavioural in nature. These enable them to live successfully in their habitat.
There are three modes of adaptation:
Structural Adaptation
Adaptive colouration
Behavioural Adaptation
This is a special modification of structures which help organisms to survive better in their environment. Examples include;
Structural adaptation to obtain food e.g. a toad has a long tongue to catch its prey; birds have sharp, strong and curved claws for catching their prey; Insects have modified mouth parts for feeding; Insectivorous plants (e.gutriculariaspi.e. bladderwort, Droseriasp i.e. sundew, etc) have special structural adaptive features.
Structural adaptation for escape and defence. Escape adaptation can be grouped into camouflage (concealing ccolouration), individual and group responses e.g. caterpillars taking the colour of leaves. Defence adaptation may be inform of physical structure e.g. spines and shell, scales etc, chemical defence e. g. snakes attack their enemies by spitting venom, bees and scorpion have stings and mimicry (looking like an uninteresting objects) e. g. stone plant.
Structural adaptation to attract matese.g. Adult male agama lizard displays its bright colour to attract its mates, flowering plants attract insects for pollination, bright coloured feathers of male domestic fowls and peacock etc.
Structural adaptation to regulate body temperature e.g. mammals have fat layer, sweat gland, feathers and subcutaneous fat in birds in birds etc. All serve to regulate heat loss.
Structural adaptation for water conservation: e.g. some plants have small needle like leaves (conifers), thick bark (acacia), waxy cuticles etc to reduce the rate of transpiration. Likewise some animals possess scales, exoskeleton, feathers etc. to reduce water loss.
This is the possession by an organism of a colour which enables it to catch its prey, avoid its predators or enemies, secure mates and ensure their survival. Adaptive colouration may be grouped into
Concealing (cryptic) colouration to help organisms blend with their background and remain unnoticed by predators
Colour blendingwith the environment e. g. green cuticles of grasshopper, green snakes etc.
Counter shading by animals possessing a dark dorsal surface and light ventral surface as in tilapia fish to remain unnoticed by predator above and below.
Colour change(camouflague)to match the environment as in chameleon, grasshopper etc.
Disruptive colouration as patterns to break the body outline of animals against the dark and light shades of their backgroung as in giraffe, leopard, tiger, lady bird beetle etc.
Warning colouration to announce the presence of the organism(s) to potential predator to avoid them because they have some unpleasant features e. g. variegated grasshoppers, black and yellow bands of wasps.
Mating colouration as in male agama lizard, peacock.
Mimicry in harmless organisms resembling a distasteful or harmful one for the enemies to avoid such e.g. stick insects, swallow tail butterfly.
Bright colouration of insect pollinated flowers and pitchers of insectivorous plants.
Behaviour is basically adaptive, everything used by organisms to promote their survival. Examples include:
Behavioural adaptation in predators e.g. Lion with high speed chases its prey; spider spins its webs for its prey
Behavioural adaptation to protect prey from predators e.g bats hold tree branches with heads upside down (which is described as swaying in the air), Antelopes escape with speed, beetles secreate offensive odour, toad puffs itself up
Behaviuoral adaptation for avoiding harsh weather conditions e.g. aestivation i.e. passive period of existence. It is practiced by crocodiles; Hibernation i.e. sleep period to survive food scarcity or winter (low temperature) exhibited by insect-eating bats; migration of certain animals (e.g cattle egrets) to favourable habitats
Behavioural adaptation in plants: e.g some plants shed leaves in dry season (deciduous plants); some like yam tuber, potatoe die down and survive as underground stem; plant seeds can remain dormant, plant shoot moves towards light (Positive phototropism)
Gregarious behaviour (movement in groups) is expressed by elephants zebra, birds, fishes, social animals (bees, termites) etc.
Social animals are those in which individuals of the same species live together cooperatively in organized communities known as societies (colonies). Examples of social animals are: social insects (like termites, honey bees or wasps, ants etc), wolves, foxes, baboons etc.
Characteristics of Social Insects
They live together
They display division of labour
They show distinct castes
Members communicate with one another within the colony.
Habitats of termites: They are found living together in large communities in nest which may be tunnels in dead wood or ant hills (termitaria).
Note– Termites are blind: they communicate through touch and smell.
They have three castes: The reproductive, soldiers, workers.
The reproductive are of three types: king, queen and winged reproductive. The king has no wing, is smaller than the queen and it fertilizes the queen. The queen has a small head, small thorase and large abdomen. It is the largest of all the castes. Only one queen at a time is found in a colony. The queen lays eggs. The winged reproductive are fertile and are potential kings and queens of new colonies.
The soldiers are sterile, wingless and blind. They have big heads with stony maxillae and mandibles. Soldiers are of two types: (i) The mandibulate soldiers with strong mandibles and (ii) Nasute soldiers with projective mouth paths. The soldiers defend the colony against enemies.
The workers are wingless, blind, and sterile. They form the majority in the colony and possess well developed mouth paths. They build and repair the termitaria; provide food for colonial members; look after the eggs laid by the queen and baby termites (nymphs).They feed the nymphs and the queen and cultivate fungus gardens.
Termites exhibit incomplete metamorphosis i.e.
Egg nymph adults
The nymphs develop into soldiers and reproductive. And those which fail to develop become workers. When the winged reproductives are mature, they exhibit nuptial or wedding flight i.e. swarming out from the existing colony to build new ones.
They move in groups to ward off their enemies
They have a wide variety of diet; feeding on both living and dead plants.
They burrow into the soil or wood to build tunnels for protection against their enemies.
The habit of feeding on dead members helps to keep the colony clean.
Their ability of massive production of off springs promotes their survival.
Termites while building their tunnels help in loosening and mixing the soil.
They decompose wooden materials as they feed.
They add humus to the soil through their decomposition activities.
They act as good source of protein and fat.
The ant hill clay can be used to build the surface of tennis court.
Habitat of Honey bees – These are social insects living in hives made up of chambers or cell.
Castes of honey bees
The bee colony has 3 castes, namely:
The drone (in hundreds per colony)
The queen (only in 1 per colony)
The workers (in thousand per colony)
The drone is the winged with shorter abdomen than the queen but bigger than the workers. The drone mates with the queen during the nuptial flight after which it dies.
The queen is a fertile female, winged and much bigger than the workers. It is fed with royal jelly and lays egg.
The worker is a sterile female, winged and is smaller than the queen or drone. It possesses eyes and a sting. Also with modified mouth paths for collecting nectar and building the hive. The workers legs are also modified for collecting pollen grains from flowers. The workers perform a special dance called rail wagging as it locates a food source. The workers secrete wax for building the hive, ventilate the hive and clean the cells, guard the hive, make honey from nectar and pollens and feed the larvae with royal jelly or honey.
Economic importance of honey bees
They help to pollinate flowers.
They produce honey which has high nutritive and medicinal value.
ORGANIC EVOLUTION
Organic evolution is the sum total of adaptive changes from pre–existing or old forms that has taken place over a long time resulting in diversity of forms, structures and functions among organism. The basis of evolution is that all organisms have pre–existing ancestors.
Evidences of evolution
Fossil record: A fossil is an impression of a plant or an animal that lived a very long time ago. The age of fossil is determined using radioisotope dating. Fossils are normally preserved in sedimentary rocks. Depending on the source, fossil records can be referred to as geological or paleontological or archaeological or historical record.
Geographical distribution: Based on the effect of climate on all living things, variations in their forms, structures and functions can occur. After several years of isolation, organisms of one climate tend to differ slightly from organisms of another climate.
Comparative anatomy: Evolution is obvious in anatomical comparison of vertebrates. The Pisces or fishes have simple heart with one auricle and one ventricle. The amphibians have two auricles and one ventricle. Reptiles have two auricles and a partially divided ventricle. Aves and mammals have two auricles and two ventricles.
Embryological evidence: The embryo of man in the womb at different stages of development resembles the embryo of fish, amphibians and reptiles.
Evidence of vestigial organ: Vestigial organs are minute and incomplete organs that have no special function. Evolutionarily, these organs are believed to be once functioning e.g. appendix and rudimentary tail in man.
Evidence from domesticated animals: These include cats, dogs, hensetc which live with humans for many years.
There are three prominent theories
Jean Lamarck’s theories of use and disuse which states that Changes in the environment lead to changes in the species of organism.
The changes cause the organisms to form new structures or habits to adapt to environmental changes.
The organisms then develop specialized characters by use and disuse of organs.
Frequently used organs become well developed and the unused ones degenerate or become useless.
The well-developed or dominantly acquired characters are inheritable.
Lamarck’s theory is unacceptable to modern scientists who have proved that only characters represented on genes are inheritable not physical ones got through use and disuse.
Charles Darwin’s theory of natural selection (survival of the fittest) which states that Species of organisms can produce large number of offspring to the environment with limited resources. This then results in competition among the offspring.
The survivors must have inherited the useful traits which are passed on to the offspring at reproduction. Those that could not survive the competition die off. As the population gradually becomes better adapted to the environment, new species emerge. This theory is widely acceptable to many scientists to date.
NOTE: Both Lamarck and Darwin recognized the importance of the environment.
Based on the combination of natural selection (Darwin’s) and the genetic origin of variation. This theory states that:
There exist variations in the species population. Some of the variations have special survival advantages Individuals with favourable variations are more adaptive to their environment than others.
The individuals have to struggle for existence in the environment. The fittest contribute more offspring to the next generation than the unfit ones.The main causes of variations are mutation and recombination of genes.
Mutation is a sudden change in DNA structure leading to a change in the phenotype of the species concerned. When mutation occurs in the gene of gametes, it leads to production of new species.
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