Lesson Notes By Weeks and Term v4 - SHS 1

Lesson Video

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Performance objectives

• Identify the key factors that influence plant growth.
• Explain how light, water, nutrients, and temperature affect plants.
• Relate these factors to local agricultural practices in Ghana.

Lesson summary

Welcome, future scientists and farmers! Today, we are exploring a topic that is all around us, from the maize on our farms to the beautiful hibiscus flowers in our school compound and the mighty odum tree in the forest. We will learn about what plants need to grow strong and healthy. Understanding these factors is not just for passing exams; it is essential for our country's agriculture, our environment, and even for growing a small vegetable garden at home. By understanding how to help plants grow, we contribute to Ghana's food security and a greener environment.

Lesson notes

Before we dive in, let's understand two key terms: Growth: This is the irreversible increase in the size of a plant. We can measure it by height, mass, or number of leaves. Development: This refers to the changes a plant goes through in its life cycle, from a seed to a mature plant that can produce flowers, fruits, and new seeds. It includes germination, flowering, and fruiting.

The factors affecting plant growth and development can be grouped into two main categories: External (Environmental) Factors and Internal (Genetic) Factors. A. External (Environmental) Factors

These are conditions in the plant's surroundings. Light What it is: The primary source of energy for most life on Earth, coming from the sun. Why it's important: Light is essential for photosynthesis, the process where plants use light energy, water, and carbon dioxide to create their own food (glucose). *Equation:* 6CO₂ (Carbon Dioxide) + 6H₂O (Water) --(Light Energy / Chlorophyll)--> C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen) How it affects growth: Intensity: Bright light generally leads to a higher rate of photosynthesis and faster growth. However, too much intense light can damage the plant. A plant grown in dim light will be tall, thin, and yellowish (a condition called etiolation) as it struggles to reach for light. Duration (Photoperiod): The length of daylight affects the flowering of many plants. For example, some plants only flower when the days are short, while others need long days. Ghanaian Example: A maize plant grown in the open field under full sun will be much stronger and greener than one planted in the deep shade of a large mango tree. Water What it is: A vital liquid for all living things. Why it's important: It is a key raw material for photosynthesis. It transports dissolved mineral salts from the roots to the rest of the plant through the xylem. It helps maintain the shape and firmness of plant cells (turgor pressure). When a plant lacks water, it wilts. It is needed for seeds to germinate. Ghanaian Example: During the Harmattan season, many plants wilt or die because of the lack of rainfall and low humidity. Farmers who can irrigate their vegetable farms during this time can produce crops all year round. Temperature What it is: The degree of hotness or coldness of the environment. Why it's important: Temperature affects the rate of chemical reactions in the plant, which are controlled by enzymes. How it affects growth: Optimum Temperature: Every plant has an ideal temperature range for growth. For most tropical crops like cocoa and yam, this is between 25°C and 35°C. Low Temperature: Slows down enzyme activity, leading to slow growth. High Temperature: Can cause enzymes to lose their shape and stop working (denature), which can kill the plant. Ghanaian Example: Yam grows very well in the warm conditions of the Guinea Savannah and Forest zones but would not grow well in the cold temperatures on top of Mount Afadja during a cold night. Mineral Nutrients What they are: Chemical elements absorbed from the soil through the roots. Why they're important: They are the building blocks for creating new cells and vital compounds. We classify them into two groups: Macronutrients (needed in large amounts): Nitrogen (N): For healthy leaf growth and green colour (part of chlorophyll). Phosphorus (P): For strong root development, flowering, and fruiting. Kalassium (K): For overall plant health, disease resistance, and water regulation. *You often see N-P-K ratios on fertilizer bags.* Micronutrients (needed in small amounts): Iron, Manganese, Zinc, etc. Ghanaian Example: A cocoa farmer applies NPK 15-15-15 fertilizer to his young cocoa seedlings to ensure they get a balanced supply of the major nutrients for strong, healthy growth. If the soil lacks nitrogen, the leaves will turn yellow. Carbon Dioxide (CO₂) & Oxygen (O₂) CO₂: A gas in the air, used as a raw material for photosynthesis. It is usually readily available, but its concentration can affect the growth rate. O₂: Essential for aerobic respiration, the process where the plant breaks down the glucose it made to release energy for growth. Plant roots especially need oxygen from air spaces in the soil. If soil becomes waterlogged (filled with water), the roots can't get oxygen and the plant can die. B. Internal (Genetic) Factors

These are factors within the plant itself, determined by its DNA. Plant Hormones (Phytohormones) What they are: Chemical messengers produced by the plant that control its growth and development. Key Examples & Functions: Auxins: Promote stem elongation and control growth towards light (phototropism). Gibberellins: Promote seed germination, stem growth, and flowering. Cytokinins: Stimulate cell division and delay the aging of leaves. Ethylene: A gas that promotes fruit ripening (this is why one ripe banana in a bag will cause the others to ripen quickly). Abscisic Acid (ABA): Controls seed dormancy and helps the plant respond to stress, like closing its stomata during a drought. The Concept of Limiting Factors

Evaluation guide

• Explain the factors that affect the growth and development of flowering plants.
• Inquiry -Based Learning: r esearch on the factors that affect the growth and development of flowering
• plants. Learners learn to work independently, develop self -confidence and believe that their thoughts and
• opinions are valued.