Cambridge International Examinations G9 Biology Summary Sheet 10 (2024-2025) PDF

Academic Year 2024-2025/ First Semester Student’s Name: Subject: Biology Summary sheet no. 10 Chapter 9 Photosynthesis Grade: 9 (A, B) Lessons (1, 2, & 3) Date: /11/2024 Teacher: Marah Hammouda...

Academic Year 2024-2025/ First Semester Student’s Name: Subject: Biology Summary sheet no. 10 Chapter 9 Photosynthesis Grade: 9 (A, B) Lessons (1, 2, & 3) Date: /11/2024 Teacher: Marah Hammouda Lesson 9.1 Energy and Life (From 282 to 285) Chemical energy and ATP: Those phosphate groups are the key to ATP's ability to store and release energy. Adenosine diphosphate (ADP) is a compound that looks almost like ATP, except that it has two phosphate groups instead of three. When a cell has energy available, it can store small amounts of it by adding phosphate groups to ADP to produce ATP. Cells can release the energy stored in ATP by the controlled breaking of the chemical bonds between atoms in the second and third phosphate groups. What do cells use ATP for? One-way cells use the energy provided by ATP is for carrying out active transport. Many cell membranes contain sodium-potassium pumps, membrane proteins that pump sodium ions (Na+) out of the cell and potassium ions (K+) into it. ATP provides the energy that keeps this pump working, maintaining a carefully regulated balance of ions on both sides of the cell membrane. 1 Heterotrophs and Autotrophs: Most animals obtain the chemical energy they need from food. Organisms that obtain food by consuming other living things are known as heterotrophs. Some heterotrophs get their food by eating plants such as grasses. Other heterotrophs obtain food from plants indirectly by feeding on other animals. Still other heterotrophs obtain food by absorbing nutrients from decomposing organisms in the environment. Mushrooms obtain food this way. Plants, algae, and some bacteria are able to use energy from sunlight to synthesize food molecules. Organisms that make their own food are called autotrophs. 2  Lesson 9.2 Photosynthesis: An Overview (From 286 to 290) Chlorophyll and chloroplasts: Photosynthetic organisms use pigments to capture the energy in sunlight. The principal pigment of green plants is known as chlorophyll. The two types of chlorophyll found in plants, chlorophyll a and chlorophyll b. Chloroplasts are surrounded by two envelope membranes, and they are filled with saclike chlorophyll-containing membranes called thylakoids. These thylakoids are interconnected and arranged in stacks known as grana (singular: granum). The fluid portion of the chloroplast, outside of the thylakoids, is known as the stroma. High Energy Electrons: An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule. One of these carrier molecules is a compound known as NADP+. NADP+ accepts and holds two high-energy electrons, along with a hydrogen ion (H+). This converts the NADP+ into NADPH.. An Overview of Photosynthesis: Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into sugars and oxygen (products). 3 Stages of Photosynthesis: Photosynthesis actually involves two sets of reactions. 1) Light-dependent reactions: The first set of reactions is known as the light-dependent reactions because they require the direct involvement of light and light-absorbing pigments. The light-dependent reactions take place in thylakoid membranes and use energy from sunlight to add a third phosphate to ADP to make ATP. 2) Light-independent reactions: Plants absorb carbon dioxide from the atmosphere and complete the process of photosynthesis by producing carbon-containing sugars and other carbohydrates. During the light-independent reactions, the ATP and NADPH molecules produced in the light-dependent reactions are used to build high-energy sugars from carbon dioxide. As the name implies, no light is required to power the light-independent reactions, which take place outside the thylakoids, in the stroma of the chloroplast. 4  Lesson 9.3 The Process of Photosynthesis (From 291 to 297) 1) Light-Dependent Reactions Photosystems: clusters of chlorophyll and proteins. An electron transport chain: is a series of electron carrier proteins. 1. Chlorophyll in the chloroplast absorbs light. 2. The absorption of light raises electrons in chlorophyll to a higher energy level. These high energy electrons (e-) are passed from chlorophyll to the electron transport chain. 3. On the inner surface of the thylakoid membrane, water is pulled apart. For every water molecule pulled apart, two electrons, two hydrogen ions (H +), and one oxygen atom (O) are produced. The electrons from water replace the electron in chlorophyll that moved to the electron transport chain. The oxygen is released to the air. 4. As the high-energy electrons move down the electron transport chain, their energy is used to pump more H+ ions into the thylakoid space. The energy of the electrons decreases, similar to a battery being drained as it is used. 5. Pigments in photosystem I use energy from light to reenergize the electrons and pass them to other carriers and eventually to the electron carrier NADP +. 6. At the end of a short second electron transport chain, NADP + in the stroma picks up the high-energy electrons, along with H+ ions, at the outer surface of the thylakoid membrane, to become NADPH. 7. Hydrogen ions have been collecting on the inside of the thylakoid space. The concentration difference (gradient) between the thylakoid space and the stroma powers the spinning of ATP synthase. This powers the conversion of ADP to ATP. Summary of Light-Dependent Reactions: These reactions use light energy and water to produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH. 5  2) Light-Independent Reactions (Calvin Cycle) 1. Carbon dioxide is absorbed from the air into the chloroplast. 2. Six carbon dioxide (CO2) molecules are combined with six 5-carbon molecules already present within the stroma of the chloroplast. This produces twelve 3-carbon compounds. Enzymes facilitate this step. 3. The energy from ATP and NADPH produced in the light-dependent reactions is used to convert the twelve 3-carbon molecules into forms with more chemical energy. 4. Two of the high energy 3-carbon molecules are removed from the cycle. These molecules are what will be used to produce sugars, lipids, amino acids, or other organic compounds needed by the plant. 5. The remaining (10) 3-carbon molecules are converted back to (6) 5-carbon molecules. The 5-carbon molecules will enter the cycle again, combining with a new set of absorbed carbon dioxide molecules. Factors affecting photosynthesis: Temperature, Light, and Water The reactions of photosynthesis are made possible by enzymes that function best between 0°C and 35°C. 6