Grade 10 general science Life Science – Plant growth and development Notes

1. Explain the meaning of growth and development in plants.
2. Describe the causes of seed dormancy in plants.
3. Investigate the conditions necessary for germination.
4. Differentiate between epigeal and hypogeal germination.
5. Distinguish between primary and secondary growth in plants.
6. Describe factors that contribute to growth and development in plants.
7. Describe the role of growth hormones in plants.
8. Appreciate the concept of growth and development and its importance.

1. Growth and development — meaning

- Growth: an irreversible increase in size, mass or number of cells (for example elongation of a shoot, increase in root length, or thicker stems). Measured (height, mass, number of leaves).
- Development: progressive changes in form and function as a plant matures (germination → seedling → vegetative growth → flowering → fruiting). Development includes differentiation and ageing.

2. Seed dormancy — causes and examples

• Hard seed coat: impermeable coat prevents water entry (many legumes). Farmers often scarify or soak such seeds before planting.
• Immature embryo: seed shed before embryo fully developed (some wild species).
• Chemical inhibitors: substances (e.g., abscisic acid) in seed tissues that prevent germination until leached or broken down.
• Environmental cues required: some seeds require specific temperature cycles, light/dark conditions, or smoke/fire to break dormancy (savanna species respond to smoke/heat).

Example (Kenyan context): Many farmers pre-soak common bean seeds to soften hard seed coats and speed germination. Some grasses and savanna trees respond to fire/smoke.

3. Conditions necessary for germination (investigation)

Seeds need several conditions for germination:

• Water — to swell the seed and activate enzymes.
• Oxygen — for respiration (energy for growth).
• Suitable temperature — speeds enzyme activity (different species have different optimal ranges).
• Light or darkness — some seeds require light (small seeds), others germinate in darkness.

4. Epigeal vs hypogeal germination

Key difference: position of cotyledons after germination.

5. Primary and secondary growth

Primary growth:

• From apical meristems (tips of roots and shoots).
• Gives increase in length (roots penetrate soil, shoots reach light).
• Occurs in all plants.

Secondary growth:

• From vascular cambium and cork cambium.
• Gives increase in thickness (woody stems and roots).
• Typical of many dicot trees and shrubs (e.g., mango, Grevillea, indigenous Kenyan trees).

Observation idea: cut a young stem and a tree branch to compare rings (secondary growth) — supervised activity only.

6. Factors that contribute to growth and development

• Genetic makeup (species-specific potential).
• Water supply and soil moisture.
• Nutrients (nitrogen, phosphorus, potassium, micronutrients).
• Light quality and duration (photoperiod affects flowering).
• Temperature (affects metabolism and enzyme activity).
• Soil aeration and oxygen supply.
• Pest and disease pressure; competition (weeds).
• Human practices: planting time, spacing, fertiliser application, pruning.

7. Plant growth hormones and their roles

• Auxins — cell elongation, phototropism, apical dominance; used in rooting powders.
• Gibberellins (GAs) — stimulate seed germination, stem elongation, break dormancy.
• Cytokinins — promote cell division, delay leaf senescence, work with auxins for organ formation.
• Abscisic acid (ABA) — promotes dormancy, closes stomata in drought.
• Ethylene — involved in fruit ripening and leaf/flower drop (abscission).

Practical note: farmers soak seeds, use growth regulators occasionally, or prune to change hormone balance and branching.

8. Importance / appreciation

Understanding plant growth and development helps in:

• Improving crop yields (timing of planting, fertiliser use).
• Managing seed handling and breaking dormancy when needed.
• Forestry and tree planting (selecting species with suitable growth patterns).
• Conservation and restoration — know how seedlings establish in local ecosystems.

Suggested learning experiences (classroom & practical)

1. Practical germination tests (see investigation above). Use locally available seeds: common bean, maize, pigeon pea or cowpea.
2. Compare epigeal vs hypogeal germination by germinating a bean and maize seed side by side; photograph daily and prepare a short report.
3. Demonstrate seed dormancy-break methods: soaking (beans), scarification with sandpaper for hard-coated seeds, and discuss smoke/heat cues for savanna species (theory or demonstration if safe).
4. Measure primary growth: plant seedlings and measure shoot and root length weekly to plot a growth curve; relate to watering and light treatments.
5. Visit a local farm or nursery: observe young trees and crops, discuss management practices that affect growth (spacing, pruning, fertiliser).
6. Group research task: pick a Kenyan crop (maize, beans, tea, sugarcane) and present how knowledge of hormones/growth can improve production.
7. Do a simple cambium/secondary growth demonstration using cross sections of woody stems (teacher-prepared slides or images) to show growth rings.

Assessment ideas: short quizzes (definitions), ask learners to design a germination experiment (variables, controls), and practical reports with simple data tables and graphs.

• Define growth and development in plants.
• Name three causes of seed dormancy and one method to break each.
• List four conditions needed for germination.
• Explain the difference between epigeal and hypogeal germination with one Kenyan example of each.
• Contrast primary and secondary growth and give an example of a plant showing secondary growth.
• Name 3 plant hormones and one role each plays.