Grade 10 general science – Plant growth and development Quiz

1. Which process in plants converts light energy into chemical energy stored as sugars?

Respiration
Nitrogen fixation
Transpiration
Photosynthesis
Explanation:

Photosynthesis is the process by which plants use light energy, carbon dioxide and water to produce sugars and oxygen. Respiration breaks down sugars, transpiration is water loss, and nitrogen fixation converts atmospheric nitrogen to usable forms.

2. What is the main function of root hairs in young maize or bean plants grown in Kenyan farms?

Store pollen for fertilization
Produce flowers for reproduction
Conduct photosynthesis to supply extra energy
Increase surface area for water and mineral absorption
Explanation:

Root hairs are tiny extensions of root epidermal cells that increase surface area, improving uptake of water and dissolved minerals from the soil.

3. During seed germination, which of the following is the first event for most seeds like maize after they absorb water?

Leaves expand fully
Radicle (root) emerges
Flower buds form
Fruit develops
Explanation:

After water uptake (imbibition), the radicle usually emerges first to anchor the seedling and absorb water and nutrients, allowing further growth of shoot and leaves.

4. Which plant hormone is mainly responsible for promoting stem elongation and growth in young seedlings?

Auxin
Cytokinin
Ethylene
Abscisic acid
Explanation:

Auxins stimulate cell elongation in stems and are important for phototropism and apical dominance. Ethylene affects ripening, abscisic acid promotes dormancy, and cytokinins promote cell division.

5. What is phototropism in plants?

Exchange of gases in the stomata
Growth of a plant toward or away from light
Movement of pollen by wind
Loss of water vapour from leaves
Explanation:

Phototropism is directional growth in response to light, commonly seen when shoots bend toward light due to unequal distribution of auxin.

6. Which stage comes immediately after pollination in flowering plants such as tea or coffee?

Fertilisation
Germination
Photosynthesis
Seed dispersal
Explanation:

After pollination (transfer of pollen to the stigma), fertilisation occurs when sperm from pollen fuses with the ovule to form a zygote, leading to seed development.

7. Which mineral nutrient is most directly needed for strong stems and seeds and is commonly applied as phosphate fertilizer to Kenyan soils?

Iron
Potassium
Phosphorus
Nitrogen
Explanation:

Phosphorus is important for energy transfer, root development and seed formation; phosphate fertilizers supply phosphorus to soils where it is limiting.

8. What role do guard cells play in a leaf?

Control opening and closing of stomata for gas exchange and transpiration
Synthesize chlorophyll in the chloroplasts
Absorb nutrients from the soil
Transport water up the xylem vessels
Explanation:

Guard cells change shape to open or close stomatal pores, regulating carbon dioxide uptake for photosynthesis and water loss through transpiration.

9. Which environmental factor most directly affects the rate of transpiration in plants on a hot, dry Kenyan afternoon?

Humidity and temperature
Soil pH
Soil type only
Root length only
Explanation:

Transpiration rate increases with higher temperature and lower humidity because the water vapour gradient between leaf and air becomes larger; soil pH and root length are less directly influential on immediate transpiration.

10. What is photoperiodism and why is it important for Kenyan farmers growing short-day crops?

Plants' response to the length of day or night, determining flowering time
Movement of water through the plant
The process of leaves falling off in dry season
The rate at which plants respire at night
Explanation:

Photoperiodism is how plants detect daylength to time flowering. Short-day crops flower when nights are long; understanding this helps farmers in timing planting for local rainy seasons.

11. Which structure transports sugars produced in leaves to other parts of the plant such as roots and developing fruits?

Phloem
Xylem
Mesophyll
Epidermis
Explanation:

Phloem conducts dissolved sugars (products of photosynthesis) from leaves to sinks like roots, shoots and fruits; xylem mainly transports water and minerals upward.

12. Why is crop rotation practiced by farmers in Kenya?

To reduce soil nutrient depletion and control pests and diseases
To prevent any plant growth on the land
To increase soil salinity on purpose
To ensure the same crop is grown continuously for higher yield
Explanation:

Rotating different crops helps restore nutrients (e.g., legumes add nitrogen), breaks pest and disease cycles, and maintains soil health for sustained yields.

13. What is the main purpose of pruning fruit trees like mango or avocado in Kenyan orchards?

Improve light penetration and air circulation to increase fruit quality and yield
Increase transpiration by removing leaves
Prevent photosynthesis from occurring
Stop the tree from producing flowers
Explanation:

Pruning removes excess branches to allow more light and air into the canopy, reducing disease and improving fruit development and harvestability.

14. Which of the following best explains why seeds are dispersed away from the parent plant?

To ensure the seeds return to the parent plant
To prevent pollination
To make seeds heavier and less likely to germinate
To reduce competition for light, water and nutrients between parent and seedlings
Explanation:

Dispersal helps offspring establish where resources are available and reduces competition with the parent, improving survival chances.

15. How does adding compost to farm soil help plant growth?

Prevents root growth entirely
Makes soil completely waterproof
Improves soil structure, water retention and supplies nutrients
Eliminates the need for sunlight
Explanation:

Compost adds organic matter that enhances soil texture, increases the soil’s ability to hold water and nutrients, and supplies slow-release nutrients for plants.

16. Which gas is taken in by leaf stomata for photosynthesis and which gas is released as a major by-product?

Nitrogen is taken in and carbon dioxide is released
Methane is taken in and nitrogen is released
Carbon dioxide is taken in and oxygen is released
Oxygen is taken in and carbon dioxide is released
Explanation:

During photosynthesis, plants take in carbon dioxide from the air and produce oxygen as a by-product while forming sugars.

17. What is the primary function of mycorrhizal fungi associated with plant roots in Kenyan soils?

Produce toxic compounds to kill the plant
Block root growth completely
Increase uptake of water and phosphorus in exchange for sugars
Cause immediate wilting of the plant
Explanation:

Mycorrhizae form mutualistic associations with roots, extending the effective root area to access water and nutrients (especially phosphorus) while receiving carbohydrates from the plant.

18. Which agricultural practice helps conserve soil moisture and reduce erosion on sloping farmland in Kenya?

Removing all vegetation cover
Frequent ploughing across the slope
Terracing and mulching
Burning crop residues after harvest
Explanation:

Terracing reduces slope steepness and runoff, and mulching covers soil to retain moisture and protect against erosion; burning and removing cover increase erosion risk.

19. Why do some plants like certain sorghum varieties close their stomata during the hottest part of the day?

To absorb more sunlight for photosynthesis
To increase water loss and cool the plant quickly
To release stored sugars into the air
To reduce water loss through transpiration and conserve water
Explanation:

Closing stomata limits water loss when evaporative demand is high, helping the plant conserve water though it reduces CO2 uptake and photosynthesis temporarily.

20. What causes phototropism, the bending of plant shoots toward light?

Equal growth on both sides of the stem
Gravity acting stronger on one side
Roots pulling the shoot toward the soil
Uneven distribution of auxin causing cells to elongate more on the shaded side
Explanation:

Auxin accumulates on the shaded side of a shoot, promoting cell elongation there so the shoot bends toward the light source.

21. Which condition would most likely break seed dormancy and allow germination of many crop seeds?

Freezing temperatures only
Adequate water, oxygen and suitable temperature
Continuous darkness at very high temperatures
Complete absence of water and oxygen
Explanation:

Seeds require water to rehydrate metabolic systems, oxygen for respiration and a suitable temperature to activate enzymes; without these, dormancy persists.

22. What is the effect of applying too much nitrogen fertilizer to a vegetable crop?

Excessive leafy growth with poor flowering and possible nutrient imbalance
Complete elimination of soil water
Immediate increase in root depth only
Improved fruit set with no side effects
Explanation:

High nitrogen encourages vegetative (leaf) growth, which can reduce flowering and fruiting and may cause imbalances and increased susceptibility to pests and lodging.

23. Which adaptation helps plants survive in waterlogged soils common in some parts of flood-prone Kenyan lowlands?

Aerenchyma tissues that allow oxygen movement to submerged roots
Producing only deep taproots with no lateral roots
Closing all stomata permanently
Removing all leaves to reduce photosynthesis
Explanation:

Aerenchyma are air-filled spaces in roots and stems that permit diffusion of oxygen from shoots to roots, helping plants survive low-oxygen waterlogged conditions.

24. How does salinity in soil affect plant growth often seen in irrigated fields?

Increases the ability of roots to absorb unlimited water
Reduces water uptake by roots and can cause leaf burn and stunted growth
Removes the need for photosynthesis
Makes plants resistant to all diseases
Explanation:

High salt concentration in soil makes it harder for roots to take up water (osmotic stress) and can lead to ion toxicity, leaf scorch and reduced growth.

25. Which method best demonstrates an experiment a Form 3 Kenyan student can do to investigate the effect of light on plant growth?

Planting seeds in different types of soil but keeping all light equal
Growing identical seedlings under different light conditions (full light, shade, darkness) and comparing height and leaf development
Measuring rainfall only and not observing plants
Mixing random chemicals into the soil without control
Explanation:

This controlled experiment isolates light as the variable; using identical seedlings and conditions except for light allows comparison of its effect on growth metrics.

26. Why is nitrogen fixation by legume roots important in sustainable farming systems in Kenya?

It prevents water from entering the soil
It causes seeds to become sterile
It immediately kills pests attacking the crop
It supplies usable nitrogen to the soil, reducing the need for artificial fertilizers
Explanation:

Rhizobium bacteria in legume root nodules convert atmospheric nitrogen into forms plants can use, improving soil fertility and lowering fertilizer costs.