Describe excretion in plants and the uses of specific plant excretory products.

Here are the answers to your questions: 8.1 In Plants Question 1: Describe how excretion takes place in green plants. Plants excrete waste products through various mechanisms: Gaseous wastes like oxygen (from photosynthesis) and carbon dioxide (from respiration) are eliminated through stomata in leaves and lenticels* in stems via diffusion. Excess water is removed from the plant body through transpiration*, primarily from stomata. Solid and liquid wastes (e.g., organic acids, alkaloids, tannins, resins, gums, calcium oxalate crystals) are often stored in the large central vacuoles* of cells, making them inert. Some waste products accumulate in old leaves, bark, or fruits, which are then periodically shed* from the plant, removing the wastes. Certain plants also excrete some waste products into the soil* through their roots. Question 2: State one use of each of the following excretory products of plants: a) colchicine: Used in plant breeding* to induce polyploidy (doubling the number of chromosomes). b) papain: Used as a meat tenderizer* and in digestive aids. Question 3: Explain why plants do not require specialized excretory organs. Plants do not require specialized excretory organs because: They have a lower metabolic rate* compared to animals, producing fewer waste products. Many of their waste products, such as carbon dioxide and water, are reused* in processes like photosynthesis. They can store waste products* in non-living parts of the plant or in vacuoles, rendering them harmless. They shed parts* like leaves and bark that accumulate waste, effectively removing it from the plant body. Gaseous wastes are eliminated through simple diffusion* via stomata and lenticels. Question 4: State one economic importance of each of the following plant excretory products. a) Tannin: Used in leather tanning* and in the production of ink. b) Quinine: Used as an anti-malarial drug*. c) Caffeine: Used as a stimulant* in beverages like coffee and tea. Question 5: How does excretion take place in plants? Excretion in plants occurs through: Gaseous exchange*: Oxygen and carbon dioxide are released through stomata and lenticels. Transpiration*: Excess water is lost as vapor from leaves. Storage*: Waste products are stored in vacuoles or non-living parts like heartwood. Shedding*: Wastes accumulated in old leaves, bark, and fruits are removed when these parts fall off. Exudation*: Some wastes are released into the soil through roots. Question 6: State one use of each of the following excretory products of plants: a) colchicine: Used to induce polyploidy* in plants for breeding purposes. b) papain: Used as a meat tenderizer*. Question 7: State two ways by which plants manage their solid wastes. Plants store solid wastes in vacuoles* within their cells, making them inert. They deposit solid wastes in old leaves, bark, or fruits*, which are then shed from the plant body. Question 8: Describe how plants eliminate waste products. Plants eliminate waste products through several methods: Gaseous wastes: Oxygen produced during photosynthesis and carbon dioxide from respiration are released into the atmosphere through stomata (pores on leaves) and lenticels* (pores on stems) via diffusion. Water: Excess water is eliminated primarily through transpiration, where water vapor evaporates from the stomata. Some plants also exhibit guttation*, releasing liquid water droplets from leaf margins. Storage in vacuoles: Many metabolic by-products, such as organic acids, alkaloids, tannins, resins, gums, and mineral crystals (e.g., calcium oxalate), are stored in the large central vacuoles* of plant cells. These substances are often rendered harmless or inert in this state. Shedding of parts: Waste products can accumulate in specific parts of the plant, such as old leaves, bark, or fruits*. When these parts are shed periodically, the accumulated wastes are effectively removed from the plant body. Excretion into the soil: Some plants release certain waste products, such as excess mineral salts or organic compounds, into the surrounding soil* through their roots. 8.2 In Animals Question 1: Explain how the mammalian skin is adapted to perform its functions. The mammalian skin is adapted to perform various functions: Protection: The epidermis is a tough, stratified squamous epithelium, with its outermost layer (stratum corneum) being keratinized*, providing a waterproof barrier against pathogens, chemicals, and physical injury. Melanin* pigment, produced by melanocytes in the epidermis, protects against harmful ultraviolet (UV) radiation. Hair* provides insulation and protection from UV light and minor abrasions. Sebaceous glands secrete sebum*, an oily substance that lubricates the skin and hair, making it waterproof and possessing antibacterial properties. The subcutaneous layer (hypodermis) contains adipose tissue* (fat), which acts as a cushion against physical trauma. Temperature Regulation (Thermoregulation): Sweat glands produce sweat*, which cools the body as it evaporates from the skin surface. Blood vessels in the dermis can dilate (vasodilation) to increase blood flow to the skin surface, enhancing heat loss, or constrict (vasoconstriction)* to reduce blood flow and conserve heat. Hair traps a layer of air close to the skin, providing insulation. Arrector pili muscles* contract to make hair stand erect, increasing the trapped air layer (piloerection). The adipose tissue* in the hypodermis acts as an insulating layer, preventing heat loss. Sensory Perception: The skin is richly supplied with various nerve endings and sensory receptors* (e.g., Meissner's corpuscles for touch, Pacinian corpuscles for pressure, free nerve endings for pain and temperature) that detect external stimuli. Excretion: Sweat glands* excrete small amounts of metabolic wastes such as water, salts, urea, and lactic acid. Vitamin D Synthesis: The skin contains a precursor molecule that is converted into Vitamin D* upon exposure to ultraviolet (UV) light from the sun, which is crucial for calcium absorption. Storage: The subcutaneous layer stores fat* (adipose tissue) as an energy reserve. Question 2: Give reasons for the following: a)* Constant body temperature is maintained in mammals. Mammals maintain a constant body temperature (are homeothermic) to ensure that enzymes and other metabolic processes function optimally within a narrow temperature range, allowing for efficient and stable physiological activities regardless of external temperature fluctuations. Question 3: The temperature of a person was taken before, during and after taking a cold bath. The results are shown in the graph below. a)* Explain why the temperature fell during bath. The body temperature fell during the cold bath because the cold water had a much lower temperature than the body. Heat was rapidly lost from the body to the water through conduction and convection, causing the body's core temperature to decrease. b)* What changes occurred in the skin that enabled the body temperature to return to normal? To return to normal temperature, the skin's blood vessels underwent vasoconstriction, reducing blood flow to the surface to minimize heat loss. Additionally, shivering (involuntary muscle contractions) would have occurred to generate heat