Plant Nutrition
Photosynthesis is the process by which plants manufacture carbohydrates from raw materials using energy from light.
Write the balanced chemical equation for photosynthesis. [2 marks]
Name the green pigment found in plant cells that absorbs light energy for photosynthesis. [1 mark]
CO2 + 6H2O --light & chlorophyll --> C6H12O6 + 6O2 [2] (1 mark for correct formulas, 1 mark for correct balancing)
Chlorophyll [1]
Match each nutrient deficiency to its associated deficiency disease:
Vitamin C
Vitamin D / Calcium
Iron
Vitamin C -> Scurvy [1]
Vitamin D / Calcium -> Rickets [1]
Iron -> Anaemia [1]
Plants have specialized transport tissues called xylem and phloem.
State the substance transported by xylem and the direction of transport. [2 marks]
State the substances transported by phloem and name this transport process. [2 marks]
Xylem: Water and mineral ions [1], upwards from roots to leaves [1].
Phloem: Sucrose and amino acids [1], process is called translocation [1].
Name the four main chambers of the human heart. [2 marks]
Name the main blood vessel that carries oxygenated blood away from the left ventricle to the rest of the body. [1 mark]
Right atrium, right ventricle, left atrium, left ventricle [2] (1 mark for atria, 1 mark for ventricles).
Aorta [1].
Define the term pathogen. [1 mark]
State two mechanical barriers and one chemical barrier the human body uses to defend against pathogens. [3 marks]
A disease-causing organism [1].
Mechanical barriers: Skin [1], Nose hairs [1]. Chemical barrier: Hydrochloric acid in stomach or mucus / lysozymes [1].
Leaves are adapted to carry out photosynthesis efficiently.
Name the tissue layer in a leaf where the highest rate of photosynthesis occurs. [1 mark]
Describe two structural adaptations of this layer that maximize light absorption. [2 marks]
Palisade mesophyll [1]
Any two:
Cells are tightly packed near the upper surface to absorb maximum light [1].
Cells are column-shaped / elongated vertically to maximize light capture [1].
Contains a very high concentration of chloroplasts [1].
State the organ that secretes each enzyme and the end-products of digestion for each:
Amylase
Lipase
Amylase: Secreted by salivary glands or pancreas [1]; converts starch to maltose / glucose [1].
Lipase: Secreted by pancreas [1]; breaks down fats into fatty acids and glycerol [1].
Explain how root hair cells absorb water from the soil solution. [3 marks]
Soil water has a higher water potential than the cytoplasm of the root hair cell [1].
Water enters the cell by osmosis [1].
Across a partially permeable membrane down a water potential gradient [1].
Compare the structural features of arteries and veins in term of
- Wall thickness
- Size of lumen
- Valves present
(6)
Artery: Thick muscular/elastic walls [1], Narrow lumen [1], No valves present (except semi-lunar at heart base) [1].
Vein: Thin walls [1], Wide lumen [1], Valves present to prevent backflow [1].
White blood cells form an essential part of the internal immune response.
Describe the function of phagocytes in defending against pathogens. [2 marks]
Describe the function of lymphocytes in defending against pathogens. [2 marks]
Phagocytes: Engulf pathogens (phagocytosis) [1] and digest them using digestive enzymes [1].
Lymphocytes: Produce specific antibodies [1] that bind to complementary antigens on pathogens [1].
Plants require inorganic ions absorbed from the soil to maintain healthy growth.
State the mineral ion required to synthesize chlorophyll. Describe the symptom if a plant lacks this ion. [2 marks]
State the mineral ion required to synthesize amino acids and proteins. Describe the symptom of a deficiency in this ion. [2 marks]
Magnesium ions [1]; deficiency causes yellowing between leaf veins (chlorosis) [1].
Nitrate ions [1]; deficiency causes stunted growth / yellow older leaves [1].
Bile is produced by the liver and stored in the gall bladder before being released into the duodenum.
State the two main functions of bile in digestion. [2 marks]
Explain how one of these functions speeds up lipid digestion by lipase. [2 marks]
Functions:
Neutralizes stomach acid (hydrochloric acid) entering the duodenum [1].
Emulsifies fats / breaks large fat droplets into small droplets [1].
Emulsification increases the surface area of fat droplets [1], allowing lipase enzymes to access and digest lipids much faster [1].
Define transpiration and describe how water travels up the xylem vessel in a continuous column. [4 marks]
Definition: The loss of water vapor from plant leaves by evaporation of water at the surfaces of mesophyll cells followed by diffusion through stomata [2].
Column movement: Evaporation at leaves creates a transpiration pull / tension that draws water upwards [1]. Water molecules stick together via cohesion, maintaining an unbroken water column [1].
Humans have a double circulation system.
Explain what is meant by a double circulation system. [2 marks]
State two advantages of a double circulation system compared to a single circulation system (such as in fish). [2 marks]
Blood passes through the heart twice for every complete circuit of the body [2] (pulmonary and systemic circuits).
Advantages:
Oxygenated and deoxygenated blood are kept separate [1].
Blood can be pumped to body tissues at a higher pressure, delivering oxygen and glucose faster [1].
Immunity can be acquired actively or passively.
Define active immunity. [2 marks]
Describe how passive immunity differs from active immunity, giving one natural example of passive immunity. [2 marks]
Defense against a pathogen by antibody production in the body [1], resulting in long-term immunity / memory cells [1].
Passive immunity is short-term defense acquired by receiving antibodies from an external source (no memory cells made) [1]. Example: Transfer of antibodies across placenta or through breast milk [1].
A glasshouse grower controls environmental conditions to maximize crop yield.
Define the term limiting factor. [2 marks]
Describe and explain how increasing light intensity affects the rate of photosynthesis up to a plateau point. [3 marks]
Something present in the environment in such short supply that it restricts the rate of a reaction [2].
As light intensity increases, the rate of photosynthesis increases because light provides the energy needed for the reaction [1]. Beyond a certain light intensity, the rate levels off / plateaus [1] because light is no longer the limiting factor (temperature or carbon dioxide concentration has become the limiting factor) [1].
The inner surface of the small intestine (ileum) is covered in millions of microscopic projections called villi.
Describe three features of a villus that adapt it for the rapid absorption of digested nutrients. [3 marks]
Name the specific structure within a villus that absorbs fatty acids and glycerol. [1 mark]
Adaptations (any three):
Epithelium is only one cell thick, creating a short diffusion path [1].
Microvilli on epithelial cells further increase surface area [1].
Dense network of blood capillaries maintains a steep concentration gradient [1].
Presence of a lacteal for lipid transport [1].
Lacteal [1].
A potometer is used to measure the rate of water uptake by a leafy shoot.
Describe the effect of increasing humidity on the rate of transpiration, and explain your answer. [2 marks]
Describe the effect of increasing wind speed on the rate of transpiration, and explain your answer. [2 marks]
Humidity: Rate decreases [1] because humid air lowers the concentration gradient of water vapor between the inside of the leaf and the outside air [1].
Wind speed: Rate increases [1] because air movement blows away water vapor around the stomata, maintaining a steep concentration gradient [1].
Explain how the heart valves ensure one-way flow of blood during a heartbeat:
Describe the action of the atrioventricular valves when the ventricles contract. [2 marks]
Explain why the wall of the left ventricle is significantly thicker than the wall of the right ventricle. [2 marks]
When ventricles contract, pressure rises, pushing the atrioventricular valves closed [1] to prevent blood from flowing backwards into the atria [1].
The left ventricle pumps blood to the entire body (systemic circulation), requiring higher pressure [1], whereas the right ventricle pumps blood a short distance to the lungs [1].
Vaccination provides active artificial immunity against specific infectious diseases.
Explain step-by-step how a vaccine protects an individual against future infection by a pathogen. [4 marks]
A weakened / harmless / dead form of a pathogen containing antigens is injected [1].
Lymphocytes recognize the foreign antigens and produce specific antibodies [1].
Memory cells are produced that remain in the bloodstream long-term [1].
If infected later by the live pathogen, memory cells produce antibodies much faster and in larger quantities, destroying the pathogen before symptoms occur [1].
Hydrogencarbonate indicator solution is used to measure changes in carbon dioxide concentration. It appears orange in normal air, yellow at high $\text{CO}_2$ concentrations, and purple at low $\text{CO}_2$ concentrations.
A student places a healthy green leaf in a sealed boiling tube containing hydrogencarbonate indicator and exposes it to bright sunlight for 4 hours.
Predict the color of the indicator after 4 hours and explain your choice in terms of gas exchange. [3 marks]
Predict the color change if the experiment is repeated in total darkness, and explain why. [2 marks]
Color: Purple [1]. Photosynthesis occurs at a faster rate than respiration in bright light [1], resulting in a net uptake of CO2 from the tube, lowering its concentration [1].
Color: Yellow [1]. In darkness, photosynthesis stops but respiration continues, releasing CO2 into the tube and raising its concentration [1].
Compare mechanical digestion and chemical digestion.
Define both terms and distinguish between their primary roles. [3 marks]
Explain how cholera bacteria cause severe diarrhea and dehydration in the human digestive system. [3 marks]
Mechanical digestion: Breakdown of large pieces of food into smaller pieces without changing the chemical molecules (e.g., chewing by teeth, churning in stomach) [1]. Chemical digestion: Breakdown of large, insoluble molecules into small, soluble molecules by enzymes [1]. Mechanical increases surface area for chemical digestion [1].
Cholera bacteria produce a toxin [1] that causes the secretion of chloride ions into the lumen of the small intestine [1]. This lowers the water potential in the gut, causing water to move out of the blood into the intestine by osmosis [1].
Translocation in phloem transports soluble organic compounds from a source to a sink.
Define the terms source and sink, giving one example of each in a growing potato plant during summer. [3 marks]
Explain how a potato tuber can act as a source at one time of the year and a sink at another time. [2 marks]
Source: Region of a plant where carbohydrates are produced / released (e.g., leaves) [1]. Sink: Region where carbohydrates are stored or used for growth/respiration (e.g., growing tubers or roots) [1]. Example: Leaves = source, growing tubers = sink [1].
In summer, leaves photosynthesize and export sucrose to tubers for storage (tuber is a sink) [1]. In early spring, stored starch in tubers is broken down into sucrose to supply growing buds before new leaves grow (tuber is a source) [1].
Coronary heart disease is a major cause of death worldwide.
Explain how a blockage in a coronary artery leads to a heart attack. [3 marks]
State three risk factors for developing coronary heart disease and describe how one of them can be managed. [3 marks]
Fatty deposits (atheroma) block the coronary artery, cutting off blood supply to heart muscle cells [1]. Heart muscle cells are deprived of oxygen and glucose [1], preventing aerobic respiration and causing cardiac muscle tissue to die [1].
Risk factors (any three): Diet high in saturated fats, stress, smoking, lack of exercise, genetic predisposition [2]. Management: Reduce saturated fat intake / exercise regularly to lower blood pressure and cholesterol [1].
Antibiotics are drugs used to treat bacterial infections, but overuse has led to antibiotic resistance.
Explain why antibiotics are effective against bacterial infections but completely ineffective against viral infections. [2 marks]
Explain how natural selection leads to a population of bacteria becoming resistant to a specific antibiotic. [3 marks]
Antibiotics target bacterial cell structures/processes (e.g., cell walls, bacterial ribosomes) [1]. Viruses lack cell walls, cell membranes, and metabolic pathways, hijack host machinery instead [1].
A random mutation gives some bacterial cells resistance to an antibiotic [1]. When exposed to the antibiotic, non-resistant bacteria die while resistant bacteria survive [1]. Resistant bacteria reproduce and pass on the resistant gene to offspring, increasing the allele frequency in the population [1].