Lesson Notes By Weeks and Term v5 - Grade 8
Photosynthesis and respiration – Week 5 focus
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Photosynthesis and respiration – Week 5 focus
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Subject: Natural Sciences
Class: Grade 8
Term: 2nd Term
Week: 5
Theme: General lesson support
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Photosynthesis and respiration are fundamental processes that sustain life on Earth. Photosynthesis is how plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose (sugar). This glucose then fuels the plant's growth and activities. Respiration, on the other hand, is how organisms, including plants and animals, break down glucose to release energy for their life processes. Understanding these processes is crucial for appreciating the interconnectedness of ecosystems and the flow of energy through them.
2.1 Photosynthesis Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct.
Equation for Photosynthesis: 6CO 2 + 6H 2 O + Light Energy → C 6 H 12 O 6 + 6O 2 Reactants: Carbon dioxide (CO 2 ), Water (H 2 O), Light Energy Products: Glucose (C 6 H 12 O 6 ), Oxygen (O 2 ) Where does it happen? Photosynthesis occurs inside organelles called chloroplasts. These are found within plant cells, especially in the leaves. Chloroplasts contain the green pigment chlorophyll, which absorbs light energy. Why is it important? Photosynthesis is the primary source of energy input into most ecosystems. It produces oxygen, which is essential for respiration in most living organisms, including humans. It removes carbon dioxide from the atmosphere, helping to regulate the Earth's climate.
Example: Consider a maize farm in the Free State. The maize plants use sunlight, water from the soil, and carbon dioxide from the air to produce glucose. This glucose fuels the growth of the maize stalks and kernels. Oxygen is released into the atmosphere. If there is inadequate sunlight or water, the rate of photosynthesis will decrease, leading to lower maize yields. 2.2 Respiration Respiration is the process by which organisms break down glucose to release energy. This energy is used for various life processes such as growth, movement, and maintaining body temperature.
Equation for Respiration: C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + Energy (ATP)
Reactants: Glucose (C 6 H 12 O 6 ), Oxygen (O 2 )
Products: Carbon dioxide (CO 2 ), Water (H 2 O), Energy (ATP - Adenosine Triphosphate) Where does it happen? Respiration mainly occurs inside organelles called mitochondria. These are found in nearly all eukaryotic cells (cells with a nucleus), including plant and animal cells. Why is it important? Respiration provides the energy that all living organisms need to survive. It releases carbon dioxide back into the atmosphere, which is used by plants for photosynthesis.
Example: Think about a cow grazing in a KwaZulu-Natal pasture. The cow eats grass (which contains glucose). Through respiration, the cow breaks down the glucose from the grass, using oxygen inhaled from the air, to produce energy. This energy allows the cow to move, digest its food, and maintain its body temperature. Carbon dioxide is released into the air. 2.3 Comparison of Photosynthesis and Respiration | Feature | Photosynthesis | Respiration | | ----------------- | ---------------------------------------------- | ---------------------------------------------- | | Energy Input | Light energy | Chemical energy (from glucose) | | Energy Output | Chemical energy (in the form of glucose) | Usable energy (ATP) | | Reactants | Carbon dioxide, Water | Glucose, Oxygen | | Products | Glucose, Oxygen | Carbon dioxide, Water | | Location | Chloroplasts (in plants, algae, some bacteria) | Mitochondria (in most eukaryotic cells) | | Occurs in | Plants, algae, some bacteria | All living organisms (plants, animals, fungi) | | Gas Exchange | Takes in CO 2 , releases O 2 | Takes in O 2 , releases CO 2 | 2.4 Interdependence of Photosynthesis and Respiration Photosynthesis and respiration are interconnected processes. The products of photosynthesis (glucose and oxygen) are the reactants of respiration. Conversely, the products of respiration (carbon dioxide and water) are the reactants of photosynthesis. This creates a cycle of energy and matter flow within ecosystems. The oxygen we breathe is created through photosynthesis, and the carbon dioxide released when we exhale is used by plants. Guided Practice (With Solutions)
Question 1: What are the reactants and products of photosynthesis?
Solution: Reactants: Carbon dioxide (CO 2 ), Water (H 2 O), Light Energy Products: Glucose (C 6 H 12 O 6 ), Oxygen (O 2 )
Commentary: This question tests the basic recall of the reactants and products of photosynthesis. Remembering the balanced equation helps with accurate answers.
Question 2: Explain why both plants and animals need to respire.
Solution: Both plants and animals need to respire because respiration is the process that releases energy from glucose. This energy is essential for all life processes, including growth, movement, reproduction, and maintaining homeostasis. Plants photosynthesize to create glucose, but they still need to respire to utilize that glucose for their own cellular activities.
Commentary: This question goes beyond simple recall, requiring an understanding of the function of respiration and its importance to all living organisms, not just animals.
Question 3: In a sealed terrarium (a closed glass container containing plants), explain how photosynthesis and respiration work together to maintain a balanced environment.