Chp 1 – Photosynthesis and the carbon cycle Topic 1.1 Photosynthesis In this picture, we see that the plant that has light is taller and greener than the one kept in the dark. They may also see that leaves of the plant in the light are broader and more numerous, and the stems are thicker. Remember that plants make food by photosynthesis, and cannot do this in the dark, so they do not have enough ‘food’ to be able to grow well. Chlorophyll is what makes plants look green, and that this is used to absorb energy from light. With no light, the plant does not make chlorophyll. Questions:- Pg no. 9 1 carbon dioxide and water 2 glucose and oxygen Questions:- Pg no. 14 3 Photosynthesis transfers energy from sunlight into chemical energy in glucose. The plant can use the glucose to make other substances. When the grasshopper eats grass, it takes in some of this energy. The lizard gets some of the energy when it eats the grasshopper. 4 Plants release oxygen into the air when they photosynthesise. Animals such as lizards need oxygen for respiration. Think like a scientist: Collecting the gas produced in photosynthesis 1 So that the gas could be collected over water. 2 So that the water plant could get energy for photosynthesis. Think like a scientist: Investigating how light intensity affects the rate of photosynthesis 1and 2 Practical based Question 3 decreases 4 increases Activity:- 1.1.2 Photosynthesis and respiration Similarities: They are both chemical reactions. They both happen inside cells. They both involve energy changes (energy transfers). They both involve glucose, oxygen, carbon dioxide and water. Differences: Respiration happens in all living cells, but photosynthesis only happens in some plant cells. Respiration happens in cytoplasm and mitochondria, but photosynthesis happens in chloroplasts. Photosynthesis needs sunlight, but respiration does not. The reactants in respiration are the products in photosynthesis, and vice versa. In photosynthesis, energy from sunlight is transferred to chemical energy in glucose. In respiration, energy in glucose is released for the cell to use. Topic 1.2 More about photosynthesis Pg no. 15 1 in the green parts/in the leaves and stem 2 because they contain chlorophyll 3 because they are not green/do not receive light Think like a scientist: Testing a leaf for starch 1-a-Starch is stored in the chloroplasts. 1-b-Boiling breaks down the cell membranes, so the iodine can reach the starch. 2This makes it easier to see the colour change when iodine solution is added. 3 Mostly, we will get a positive test result, showing that the leaf does contain starch. This was produced from the glucose that was made by photosynthesis in the chloroplasts. 4 Only the green parts contained starch. The white parts have no chlorophyll, which is needed to absorb energy from sunlight and without which photosynthesis cannot happen. Activity: Which surface of a leaf has most stomata? When we see more bubbles emerging from the lower surface of the leaf because this is where most stomata are present. The bubbles contain air. They are likely to contain a lot of oxygen if the leaf has been photosynthesising. The warm water makes the gases inside the air spaces in the leaf expand, which makes them come out of the leaf. Questions pg no. 20 1 The carbon dioxide particles have kinetic energy. They are in constant, random motion. By chance, some of them will go into the leaf through the stomata. Some will also come out. But, overall, more will go in than out because there are more of them outside the leaf than inside it. 2 Some of the oxygen diffuses out of the leaf. Some of the oxygen is used in respiration. Questions pg no.21 3 Plants get their protein by using the carbohydrates they make in photosynthesis and adding nitrogen to them to make proteins. Animals get their protein by feeding on plants and/or other animals. 4 Nitrate and magnesium are both needed for making chlorophyll, so a shortage of either of them makes leaves go yellow. Nitrate is also needed for making proteins, but without magnesium the plant cannot photosynthesise, so it has fewer carbohydrates to make proteins from. A lack of either nitrate or magnesium reduces growth. Topic 1.3 The carbon cycle The carbon dioxide in the air, contains carbon atom that is part of a compound; whereas in photosynthesis it becomes part of a glucose molecule, but it is still a carbon atom. Questions:- pg no.26 1-a-The food chain should have a correct sequence of organisms, with one plant and three animals. Arrows should go in the correct direction. For example: fig tree →wasp →spider lizard. 1-b-Yes, the arrows could also indicate how carbon atoms are transferred. Carbon is contained in the food that animals eat, in the form of compounds such as carbohydrates and proteins. 2 Proteins, carbohydrates and fats. Questions:- pg no.33 3 There would be no (or very little) combustion of fossil fuels. 4 They take a very long time to form. We are using them up much faster than they are being replenished. Think like a scientist: How do plants and animals affect carbon dioxide concentration?- Practical based answers Activity: Modelling the carbon cycle 1 No, in the real carbon cycle only some carbon atoms will move at any one point in time. 2 On stopping combustion results in fewer carbon atoms ending up in the air. Topic 1.4 Climate change Questions pg no. 34 A 3; B 1; C 3; D2 Questions pg no.39 1 An asteroid is a rock, smaller than a planet, which orbits the Sun. 2 It produced a lot of heat, which killed plants and animals close to the collision site. It produced a huge tsunami, which killed plants and animals on land that were swamped by sea water. It sent dust high into the atmosphere, so plants died because they could not photosynthesise. Animals then died because there was no food for them to eat. Questions pg no.40 3-1.3 °C 4 The temperature fell by 0.3°C between 1880 and 1910. It rose by 1.6 °C between 1910 and 2016. Questions pg no.41 5 Multiply the number of years until the end of the century by 3 mm. 6 As the mean global temperature increases, more land ice melts and adds extra water to the oceans. Also, higher temperatures cause sea water to expand. Think like a scientist: How do rising temperatures affect sea level? 1 Melting ice on land and increasing water temperature both increase the water level. Melting ice in the sea does not increase the water level. 2 They indicate how sea level is expected to rise. Activity: The carbon cycle and climate change Respiration and combustion increase the level of carbon dioxide in the atmosphere. Photosynthesis decreases it. Suggestions•Plant more trees, because they will photosynthesise and take carbon dioxide out of the air. •Stop deforestation. •Stop burning fossil fuels, to reduce combustion. •Stop using so much energy, so that we do not need to use as much fuel. Check your progress 1.1-a carbon dioxide b oxygen c soil d chlorophyll e stomata 1.2-a the type of seaweed b Any three from: the temperature; the light intensity; the size of the piece of seaweed; the time for which the apparatus is left. c the volume of gas collected (after a set period of time). 1.3-a 4 tonnes per hectare b Adding more than 60 kg per ha gives only a very small increase in yield. It is likely that the cost of the extra fertiliser would outweigh the small increase in income from selling the grain. c The wheat plants use the nitrate to make proteins. The proteins can be used to make new cells, some of which will be used to produce the grains. d In a different place, there might be a different concentration of nitrate in the soil before the fertiliser is added. There might be a lack of other minerals in the soil. The soil might be better or worse at holding water. There might be more shade in one place than another. The temperature might be different. e Magnesium is needed for making chlorophyll. 1.4-a-i-D ii-B iii-A iv-C b-i-3 ii-2 iii-1 c glucose, starch, carbohydrate, protein, fat, cellulose or chlorophyll 1.5-a Sea level will rise. There will be more extreme weather events, such as typhoons and hurricanes. b-i-Many species of organisms are completely destroyed. ii-This is due to long-term reduction in photosynthesis because of dust thrown up into the atmosphere, which reduces light penetration. This in turn reduces food for animals. Other reasons are the immediate results of the impact, including the heat and pressure wave in the vicinity of the impact, and a massive tsunami.
