Correct Answer: D. 2n → n

Correct Answer: D) competition

Explanation

When there are many organisms that live in the same area and have to compete for limited resources like food, water, and shelter, it is called competition. This means that they are all trying to get the resources they need to survive, and sometimes they may even fight for them. Competition can be between members of the same species or different species. When some organisms are better at competing than others, they may have an advantage and be more likely to survive and reproduce. The other options listed are not correct for this question. Immigration is when organisms come into an area from somewhere else. Symbiosis is when two organisms live together and both benefit from the relationship. Extinction is when all members of a certain species die out. Therefore, the correct answer to this question is option D, competition.

Explanation

(a)Role of the stomach in digestion: The stomach receives food when the sphincter at the entrance of the stomach relaxes. The muscular walls of the stomach contract and relax, to churn/mix the food, and further break down the particles. The stomach produces gastric juices, which contain dilute hydrochloric acid/pepsin/rennin. The dilute hydrochloric acid neutralizes the action of the salivary amylase, and kills bacteria present in the food. It creates a suitable condition/pH for the action of pepsin, and activates inactive pepsinogen to form pepsin. The pepsin breaks down the protein to polypeptide/peptides. While the rennin coagulates/curdles milk to enhance digestion by pepsin. The mucus produced by the stomach wall lines the wall of the stomach to prevent the action of the acid on the stomach wall. The mucus produced by the stomach lubricates the movement of the food in the alimentary canal.

(b)(i)Parts of plants where food is stored: Leaves. Stems. Roots. Seed. Fruits.

(ii)Examples:

Leaves: Onions, shallot, garlic.

Stems: Yam, sugarcane, ginger, Irish potatoes.

Roots: Cassava, carrots, sweet potatoes.

Seed: Groundnut, beans, coconut, cashew.

Fruits: Maize, guava, orange, pawpaw, cashew, palm nut, mango.

(c) Sugar regulation in mammals: The liver controls the blood glucose levels. It converts excess glucose in the blood to glycogen. The process is stimulated by the hormone insulin, which is secreted by the pancreas. When the blood glucose level falls below normal. The pancreas secretes/glucagons. This stimulates the conversion of glycogen into glucose, which is released into the blood.

Correct Answer: C. 50%

Correct Answer: A. cells

Correct Answer: B. systemic circulation

Correct Answer: A. The lymph vessels are always larger in size than the arteries

Explanation

(a) Adaptation of leaf for photosynthesis

1. Broad/flat leaf lamella, exposes large surface area for maximum absorption of light
2. Palisade mesophyll cells contain a lot of chloroplast chlorophyll; for maximum absorption of light
3. Position of leaf to stem; for optimum reception of light rays/sunlight
4. Thin lamella; allows light penetration into leaf tissue of mesophyll
5. Palisade cells are at right angle/perpendicular to the upper epidermis/chloroplasts are arranged in the periphery of the cells; all for easy activation of the chloroplasts for photosynthesis
6. Large vacuoles of the palisade cells; store photosynthetic products
7. Large intracellular air spaces in the spongy mesophyll; allow oxygen/carbondioxide to diffuse in/out of the chlorophyllus cells/ gaseous exchange
8. The epidermal cells have thin cell walls; for easy penetration of sunlight to the mesophyll
9. Guard cells have chloroplast; for the absorption of sunlight
10. The bean-shaped structure of the guard cell; is to allow for gaseous exchange
11. The stomata; open easily when it becomes turgid for diffusion of gases/carbon dioxide/oxygen
12. Xylem; conducts water into the leaves for photosynthesis
13. Phloem; transports manufactured food to other parts of the plant.

(b) Mode of feeding of tapeworm;

Parasitic mode of feeding; lives in the gut of man/pigs; has hooks/suckers; which enable it attach itself to the lining of the intestine of the host; has a flattened tape-like/ribbon-like body; provide large surface area for easy absorption of digested food; no alimentary/digestive system.

(c) Mineral elements necessary for the proper functioning of;

(i) Bones - Calcium; phosphorus; fluorine

(ii) Red blood cells - Iron; copper

(iii) Thyroid gland - Iodine.

(d) (i) Benefits of including roughages in the diet of humans :

• Stimulates bowel movement/peristalsis
• Reduces blood cholesterol/bowel cancer/gall stones/appendicitis/ obesity / diabetes mellitus
• They do not contribute to weight gain/high blood sugar
• It releases glucose slowly
• It prevents constipation.

(ii) Importance of proteins to humans;

• For the repair of damaged tissues; replacement of worn-out tissues
• For body building
• For growth
• For the supply of the necessary amino acids
• For formation of hormones/enzymes/antibodies/ forming fibrinogen necessary for blood clotting.

Correct Answer: C. Tuberculosis

Correct Answer: C. it allows utilization of soil nutrients at different levels