Respiration and Gas Exchange
Write the word equation for aerobic respiration. [2 marks]
State the primary organ where gas exchange takes place in humans. [1 mark]
glucose + oxygen -> carbon dioxide + water [2]
Lungs (or alveoli) [1]
Define the term involuntary action. [1 mark]
State the sequence of components in a standard reflex arc starting from a stimulus. [3 marks]
An automatic / unconscious response that occurs without conscious thought [1].
Stimulus -> Receptor -> Sensory neuron -> Relay neuron -> Motor neuron -> Effector -> Response [3] (Full marks for correct order).
Match each excretory organ to its primary excretory product:
Kidneys
Lungs
Skin
Kidneys -> Urea / Mineral salts / Excess water [1]
Lungs -> Carbon dioxide [1]
Skin -> Sweat (water and urea) [1]
Define asexual reproduction. [2 marks]
State one advantage of asexual reproduction in crop plants. [1 mark]
A process resulting in the production of genetically identical offspring (clones) from one parent [2].
Fast process / produces uniform crops with desirable characteristics / does not rely on pollinators [1].
State the organ in the human body where:
Sperm cells are produced [1 mark]
Egg cells (ova) are produced [1 mark]
Fertilization normally occurs [1 mark]
Testes [1]
Ovaries [1]
Oviduct (or Fallopian tube) [1]
Compare anaerobic respiration in yeast cells with anaerobic respiration in human muscle cells.
State the products of anaerobic respiration in yeast. [2 marks]
State the product of anaerobic respiration in human muscle cells. [1 mark]
Alcohol (ethanol) [1] and carbon dioxide [1].
Lactic acid [1].
Define the term synapse. [1 mark]
Describe how an impulse is transmitted across a synapse from one neuron to the next. [2 marks]
A junction between two neurons [1].
The arrival of an impulse causes the release of neurotransmitters [1], which diffuse across the synaptic gap and bind to receptors on the post-synaptic neuron [1].
Define the term homeostasis. [2 marks]
State the concept of negative feedback. [1 mark]
The maintenance of a constant internal environment [2].
A control mechanism that reverses a change to return a condition back to its set point / normal level [1].
Describe the structure of wind-pollinated flowers in term of petal, stigma and pollen grain [3 marks]
Small / green / dull / absent [1].
Feathery and hanging outside flower [1].
Smooth, light, and produced in large quantities [1].
The placenta allows exchange of substances between maternal blood and fetal blood.
Name two substances that pass from maternal blood to fetal blood. [2 marks]
Name one waste substance that passes from fetal blood to maternal blood. [1 mark]
Oxygen, glucose, amino acids, vitamins, antibodies [2] (Any two).
Urea or carbon dioxide [1].
Describe three structural features of the alveoli that adapt them for efficient gas exchange. [3 marks]
Large surface area for rapid diffusion [1].
Thin wall / single cell layer thick, providing a short diffusion pathway [1].
Dense network of capillaries, maintaining a steep concentration gradient [1].
Moist lining, allowing gases to dissolve before diffusing [1]. (Any three)
Describe how the components of the human eye adjust to focus on a near object. [3 marks]
Ciliary muscles contract [1].
Suspensory ligaments slacken / loosen [1].
Lens becomes fatter / more convex / thicker, refracting light rays more strongly [1].
Explain how the body responds to an increase in core body temperature above 37°C . [3 marks]
Vasodilation: Arterioles supplying skin capillaries dilate, increasing blood flow near the skin surface to radiate heat [1].
Sweating: Sweat glands produce sweat; evaporation of water cools the skin [1].
Hair erector muscles relax, laying hairs flat to prevent trapping an insulating layer of air [1].
Describe the process of fertilization in a flowering plant after a pollen grain lands on a compatible stigma. [3 marks]
Pollen grain germinates and grows a pollen tube down through the style toward the ovary [1].
Male gamete nucleus travels down the pollen tube and enters the ovule through the micropyle [1].
Male nucleus fuses with the female egg cell nucleus to form a zygote [1].
Describe the roles of estrogen and progesterone in controlling the menstrual cycle. [4 marks]
Estrogen:
Rebuilds / thickens the uterus lining following menstruation [1].
Stimulates the release of LH to trigger ovulation [1].
Progesterone:
Maintains the thick uterus lining for potential embryo implantation [1].
Inhibits release of FSH and LH to prevent further follicle development [1].
Describe the changes that take place in the thorax during inspiration (inhalation). [4 marks]
External intercostal muscles contract [1].
Ribcage moves upward and outward [1].
Diaphragm contracts and flattens [1].
Volume of the thorax increases, causing pressure inside the lungs to decrease below atmospheric pressure, drawing air into the lungs [1].
A plant shoot tip bends toward a unidirectional light source (phototropism).
Explain how the distribution of auxin in the shoot tip causes this response. [4 marks]
Auxin is produced at the tip of the shoot [1].
Auxin diffuses away from light toward the shaded side of the shoot [1].
Higher auxin concentration on the shaded side causes cells to elongate faster [1].
Unequal elongation causes the shoot to bend toward the light [1].
Describe how blood is filtered in the glomerulus and Bowman's capsule during urine formation. [4 marks]
High blood pressure in the glomerulus forces small molecules out of the blood [1].
Water, glucose, salts, and urea pass into the Bowman's capsule (ultrafiltration) [1].
Large molecules such as proteins and blood cells remain in the blood because they are too large to pass through [1].
Selective reabsorption takes place in the kidney tubule where all useful glucose is reabsorbed back into the blood by active transport [1].
A student investigates the environmental conditions required for seed germination.
State the three environmental factors necessary for seed germination. [3 marks]
Explain the specific role of water in seed germination. [1 mark]
Water, Oxygen, and a suitable temperature [3].
Water activates enzymes (e.g., amylase) to break down stored food reserves (starch into glucose) inside the cotyledons [1].
Compare the structure and function of human sperm cells and egg cells (ova) in term of relative size, motility, and energy store [3 marks]
Size: Sperm is very small, Egg cell is very large [1].
Motility: Sperm is motile (has flagellum), Egg cell is non-motile [1].
Energy store: Sperm has limited energy reserves, Egg cell has large yolk reserves in cytoplasm [1].
During vigorous exercise, muscle cells respire anaerobically, creating an oxygen debt.
Explain what is meant by oxygen debt and describe how the body removes lactic acid after exercise has stopped. [4 marks]
Oxygen debt is the extra oxygen required after exercise to break down accumulated lactic acid [1].
Lactic acid is transported in the blood from muscles to the liver [1].
Lactic acid is aerobically oxidized in the liver into carbon dioxide and water [1].
Breathing rate and heart rate remain elevated after exercise to supply this extra oxygen [1].
Compare the nervous system and the endocrine (hormonal) system, and explain how adrenaline prepares the body for "fight or flight". [5 marks]
Comparison:
Nervous impulses are electrical, while hormones are chemical signals transported in blood [1].
Nervous responses are faster/short-lived; hormonal responses are generally slower/longer-lasting [1].
Adrenaline effects:
Increases heart rate / pulse rate to pump blood faster [1].
Increases breathing rate to absorb more oxygen [1].
Stimulates the liver to convert glycogen to glucose, raising blood glucose levels for increased respiration [1].
Explain how the pancreas and liver work together to control blood glucose levels when:
Blood glucose concentration rises after a meal. [2 marks]
Blood glucose concentration falls during prolonged exercise. [2 marks]
When glucose rises: Pancreas secretes insulin [1]. Insulin causes liver and muscle cells to take up glucose and convert it into stored glycogen [1].
When glucose falls: Pancreas secretes glucagon [1]. Glucagon stimulates liver cells to break down stored glycogen into glucose and release it into the blood [1].
Distinguish between self-pollination and cross-pollination. [2 marks]
Discuss the potential disadvantages of self-pollination for a plant species' long-term survival in changing environments. [3 marks]
Self-pollination: Transfer of pollen from anther to stigma of the same flower or another flower on the same plant [1]. Cross-pollination: Transfer of pollen to a flower on a different plant of the same species [1].
Disadvantages:
Decreases genetic variation in the population [1].
Increases chance of offspring inheriting harmful recessive alleles [1].
Population is less able to adapt to new disease threats or changing climate conditions [1].
Human Immunodeficiency Virus (HIV) causes Acquired Immunodeficiency Syndrome (AIDS).
State two ways HIV can be transmitted between individuals. [2 marks]
Explain how HIV affects the human immune system and leads to AIDS. [3 marks]
Transmission methods:
Direct sexual contact / exchange of body fluids [1].
Sharing unsterilized hypodermic needles [1].
Across placenta during pregnancy / breast feeding [1]. (Any two)
How HIV leads to AIDS:
HIV infects and destroys lymphocytes (specifically T-helper cells) [1].
Reduced ability to produce antibodies against pathogens [1].
Immune system becomes compromised, leaving the individual vulnerable to opportunistic infections [1].