Lesson Notes By Weeks and Term v5 - Grade 8
Photosynthesis and respiration – Week 2 focus
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Photosynthesis and respiration – Week 2 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Natural Sciences
Class: Grade 8
Term: 2nd Term
Week: 2
Theme: General lesson support
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Welcome to Week 2 of our journey into the fascinating world of living organisms! This week, we'll be focusing on two crucial processes that sustain life on Earth: photosynthesis and respiration. Photosynthesis is how plants make their own food using sunlight, while respiration is how both plants and animals release energy from that food. Understanding these processes is essential because they are the foundation of all food chains and ecosystems, including those right here in South Africa. Think about the mealie fields that feed so many families, or the trees that provide shade and clean air – all of these depend on photosynthesis.
Photosynthesis: Making Food with Sunlight Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose (sugar). This glucose is the plant's food. The word "photosynthesis" itself gives a clue: "photo" means light, and "synthesis" means putting together. So, photosynthesis means "putting together with light." The Equation: The overall equation for photosynthesis is: 6CO₂ (Carbon Dioxide) + 6H₂O (Water) + Light Energy → C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen)
Explanation of the Equation: 6CO₂ (Carbon Dioxide): Plants take in carbon dioxide from the air through tiny holes in their leaves called stomata. Think of the air pollution we sometimes experience in cities like Johannesburg; plants help clean the air by using this CO2. 6H₂O (Water): Plants absorb water from the soil through their roots. South Africa is a water-scarce country, so understanding how plants use water is very important.
Light Energy: Plants capture light energy from the sun using a green pigment called chlorophyll, which is found in structures within their cells called chloroplasts. This is why plants are green! C₆H₁₂O₆ (Glucose): Glucose is a type of sugar that is the plant's food. It provides the plant with energy for growth and other processes. The plant can convert this glucose into other substances like starch for storage (e.g., in potatoes or maize). 6O₂ (Oxygen): Oxygen is released as a byproduct of photosynthesis. This is the oxygen we breathe! This is why forests and grasslands are so important – they help keep our air clean.
Factors Affecting Photosynthesis: Light Intensity: As light intensity increases, the rate of photosynthesis generally increases until it reaches a point where it plateaus. Think of a tomato plant in your garden – it will grow better in a sunny spot than in a shady one.
Carbon Dioxide Concentration: As carbon dioxide concentration increases, the rate of photosynthesis generally increases until it reaches a point where it plateaus.
Temperature: Photosynthesis works best within a certain temperature range. Too cold or too hot, and the rate of photosynthesis will decrease.
Respiration: Releasing Energy from Food Respiration is the process by which organisms break down glucose (sugar) to release energy. This energy is used for all life processes, such as growth, movement, and repair. Both plants and animals respire.
There are two main types of respiration: aerobic respiration (which requires oxygen) and anaerobic respiration (which doesn't require oxygen). We'll focus on aerobic respiration.
The Equation: The overall equation for aerobic respiration is: C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen) → 6CO₂ (Carbon Dioxide) + 6H₂O (Water) + Energy Explanation of the Equation: C₆H₁₂O₆ (Glucose): Glucose is the sugar that provides the energy. Animals get glucose from the food they eat (plants or other animals). Plants get it from photosynthesis. 6O₂ (Oxygen): Oxygen is taken in from the air. Animals breathe in oxygen, and plants take in oxygen through their stomata. 6CO₂ (Carbon Dioxide): Carbon dioxide is released as a waste product. Animals breathe out carbon dioxide, and plants release some carbon dioxide through their stomata. 6H₂O (Water): Water is also released as a byproduct.
Energy: This is the key product! The energy released is used for all life processes. The Connection Between Photosynthesis and Respiration: Photosynthesis and respiration are interconnected processes. Photosynthesis uses carbon dioxide and water to produce glucose and oxygen. Respiration uses glucose and oxygen to produce carbon dioxide, water, and energy. The products of one process are the reactants of the other! This cycle is crucial for maintaining the balance of life on Earth and for the carbon cycle.
Example 1: A maize plant in a field.
A maize plant uses sunlight, water, and carbon dioxide to produce glucose. This glucose fuels the plant's growth, allowing it to produce cobs filled with kernels that become staple food for many South Africans. Oxygen is released as a byproduct.
Example 2: A person running a marathon.
A marathon runner breathes in oxygen, which is transported to their muscles. The oxygen reacts with glucose (obtained from food) in their muscle cells to release energy. This energy powers their muscles, allowing them to run the marathon. Carbon dioxide and water are released as waste products.
Example 3: Trees in the Kruger National Park.
Trees in the Kruger National Park photosynthesize to produce their own food and oxygen. Elephants then eat those trees, getting the glucose they need for respiration. The elephants then breathe out carbon dioxide, which the trees use in photosynthesis.
Guided Practice (With Solutions)
Question 1:
What are the reactants and products of photosynthesis?