Unit 1 Plants PDF

Unit 1 Plants Presented by Seracettin Haslak 1.1 Photosynthesis The Plant use carbon dioxide and water to make glucose and oxygen. Photosynthesis is a chemical reaction. We can summarise it using a word equation: carbon dioxide + water → glucose + oxygen During photosynthesis, the plant’s...

Unit 1 Plants Presented by Seracettin Haslak 1.1 Photosynthesis The Plant use carbon dioxide and water to make glucose and oxygen. Photosynthesis is a chemical reaction. We can summarise it using a word equation: carbon dioxide + water → glucose + oxygen During photosynthesis, the plant’s leaves absorb the energy of light. The energy is stored in the glucose that is made. The glucose is a store of chemical potential energy. Photosynthesis happens inside the chloroplasts in a palisade cell like this one. Questions 1. Think back to (remember) what you have already learnt about photosynthesis. a) Where do plants get carbon dioxide from? b) Where do plants get water from? 2. Explain why photosynthesis only takes place inside chloroplasts. 1.1 Photosynthesis – Storing carbohydrates Glucose is a sugar. Sugars belong to a group of chemicals called carbohydrates. Plants usually make much more glucose than they need to use immediately. They store some of it to use later. But they do not store it as glucose. Glucose is soluble in water, which makes it difficult to store inside a cell. Instead, the plant changes some of the glucose into a different kind of carbohydrate – starch. A starch molecule is made of thousands of glucose molecules linked together in a long chain. Starch molecules are too big to dissolve in water. They stay as insoluble grains, inside the chloroplasts in the plant cell. 1.1 Photosynthesis– Testing a leaf for starch 1. Explain why the leaf needed to be boiled before testing with iodine solution. 2. Suggest why it was useful to remove the green colour from the leaf, before testing it with iodine solution. 3. Describe two things that you did in step 2 to reduce the risk of anyone being hurt. Step 2: After about two minutes, turn off the burner. This is really important, because you will use ethanol in the next step. 4. Explain why leaves often contain starch. Summary Photosynthesis is the production of glucose and oxygen, by reacting water and carbon dioxide, using energy from light. Plants often change some of the glucose into starch, for storage. Before testing a leaf for starch, you need to boil it to break down the cell membranes. 1.2 Mineral salts for plants Farmers and gardeners often add fertilisers to the soil where their crops are growing. The fertilisers provide mineral salts, which make the plants grow larger and healthier. Fertilisers contain mineral salts. These are substances that plants normally get from the soil. Plants need many different kinds of mineral salts. Two of the most important ones are nitrate and magnesium. Nitrate is needed so that the plant can make proteins. A plant that has not got enough nitrate can’t make enough proteins, so it cannot make enough new cells to grow well. 1.2 Mineral salts for plants Nitrate is also needed to make chlorophyll. If a plant does not have enough nitrate, it will become yellow instead of green. Magnesium is also needed for making chlorophyll. So a shortage of magnesium makes plant leaves go yellow. Questions 1. Give two examples of mineral salts that are needed by plants. 2. Explain why a plant that does not have enough magnesium will not grow well. 3. Think about what you know about plant roots. How do plants absorb mineral salts from the soil? Summary Plants need nitrate to make proteins, which are needed to make new cells for growth. Plants need magnesium to make chlorophyll. 1.3 Plant and water – water for support Plant cells contain a lot of water, especially inside their vacuoles. A plant cell that has plenty of water is strong and firm. When all the cells in a plant are like this, they press out against each other and make the whole plant firm and well- supported. When a plant cell doesn’t contain enough water, it becomes soft and floppy. When all the cells in a plant are like this, the plant collapses. We say that it has wilted. 1.3 Plant and water – water for transport and cooling Plants contain long tubes, called xylem, which transport water from the roots up to the leaves. There are mineral salts dissolved in the water, and this is how they are transported around the plant. When the water in the xylem gets into the leaves, it spreads out through each leaf. Some of it evaporates into the air spaces inside the leaf. When water evaporates, it absorbs heat energy. This cools down the surroundings. The water evaporating inside a plant leaf helps to keep the plant cool. This is really important for plants that live in very hot environments. 1.3 Plant and water – water for photosynthesis Water is one of the reactants in photosynthesis. Water combines with carbon dioxide, inside chloroplasts, to make glucose and oxygen. Questions 1. Explain why a plant wilts if it is short of (lacks) water. 2. How does water help a plant to keep cool? 3. Water from the soil is absorbed by a plant. Eventually, it ends up in the air as water vapour. List the parts of the plant that it passes through on this journey. 1.3 Plant and water – Water loss from plants 1. What was the variable that you changed in this experiment? 2. What variables did you keep the same? 3. Compare the change in the mass in the two plants in their pots. 4. Explain why the droplets of water formed on the inside of the plastic bag. 5. Explain the reasons for the differences between the results for the two plants. Summary Plants need water for support, cooling, transport and photosynthesis. Most of the water taken up by the roots eventually diffuses out of the plants leaves, as water vapour. 1.4 Flowers – The part of a flower Flowers are brightly coloured to attract insects and birds. They do this because the insects and birds help plants to reproduce. Flowers are the reproductive organs of plants. The petals are usually the most colourful part of the flower. They attract insects or birds to the flower. Some flowers produce scents (smells), which also help to attract insects. The insects or birds feed on sweet, sugary nectar produced at the base of the petals. They may also eat some of the pollen, produced in the anthers. The pollen contains the male gametes of the flower. The female gametes are inside the ovules, which are inside the ovaries. Unlike animals, many plants produce both male gametes and female gametes. 1.4 Flowers – The part of a flower Questions 1. Many people use the word ‘flower’ when they really mean ‘plant’. Explain the difference between a plant and a flower. 2. Insects can often smell flowers from hundreds of metres away. Suggest how the scent from the flowers spreads out into the air around them. Summary Flowers are reproductive organs of plants. The male parts of a flower are the stamens. Pollen contains the male gametes. The female parts of a flower are the ovaries, style and stigma. Ovules contain the female gametes. Petals have have bright colours and strong scents to attract Insects and birds. 1.5 Pollination Flowers do not have swimming sperm cells. Their male gametes are simply nuclei inside their pollen grains. They cannot swim. So flowers have to use another method of getting their male gametes to their female gametes. Many of them use insects or birds. Some use the wind. Pollen grains are made in the anthers of flowers. Pollen grains contain the male gametes. 1.5 Pollination – Transferring pollen grains To help the male gametes get close to the female gametes, pollen grains must be carried from the anthers (where they are made) to the stigma of a flower. Insects often help with this. When the insect comes to a flower to collect nectar, pollen gets stuck onto its body. When the insect goes to another flower, some of the pollen rubs off onto the stigma. The transfer of pollen from an anther to a stigma is called pollination. Many flowers are pollinated by insects or birds. Some, for example grasses, are pollinated by the wind. The wind blows pollen off the anthers. Just by luck, some of the pollen may land on the stigmas of other flowers. 1.5 Pollination – Transferring pollen grains Questions 1. Where are the female gametes found in a flower? 2. Where are the male gametes found in a flower? 3. Explain why plants need help to get their male gametes to their female gametes. 4. The table shows two differences between insect-pollinated and wind- pollinated flowers. Suggest reasons for these differences. Summary The male gametes of a flower are inside the pollen grains. The female gametes are inside the ovules. The male gametes cannot move by themselves, so flowers make use of insects, birds or the wind to move their pollen grains. The transfer of pollen from an anther to a stigma is called pollination. 1.6 Fertilisation In sexual reproduction, the nucleus of a male gamete and the nucleus of a female gamete join together. This is called fertilisation. When the nuclei of the two gametes have joined together, they form a new cell. This cell is called a zygote. Questions Think about what you have learnt about sexual reproduction in humans. 1. What is the name of the male gamete in humans? 2. What is the name of the female gamete in humans? 3. Where does fertilisation happen in humans? 1.6 Fertilisation – Fertilisation in a flower In flowers, the male gamete is a nucleus inside a pollen grain. The female gamete is a nucleus inside an ovule. When a flower has been pollinated, there are pollen grains on its stigma. The diagram shows how a male nucleus gets from a stigma to a female gamete. 1.6 Fertilisation – Seed formation When the male nucleus fuses with the female nucleus inside an ovule, it produces a zygote. The zygote starts to divide. It produces a little group of cells called an embryo. This embryo will eventually grow into a new plant. The ovule also begins to change. It gradually grows into a seed. 1.6 Fertilisation – Investigating seed structure Summary When a pollen grain has landed on a stigma, it grows a tube down to an ovule. The male gamete (nucleus) goes down the tube. It fuses with the female nucleus inside an ovule, producing a zygote. The zygote divides over and over again, and produces an embryo plant. The ovule becomes a seed, with the embryo plant inside it. 1.7 Fruits When an ovule develops into a seed, it is still inside the ovary. While the ovule is developing into a seed, the ovary is changing too. The ovary changes into a fruit. This means that fruits contain seeds. 1.7 Fruits - Dispersal Each plant will need water, light and mineral salts in order to grow well. If all the seeds just fell off the plant onto the ground, they would all be trying to grow in the same place. The new little plants would all have to compete with each other for water, light and mineral salts. They would have to compete with the parent plant, too. The new plants have a better chance of growing if they are in a different place. They need to be dispersed away from the parent plant. 1.7 Fruits - Dispersal Questions 1. The scientific meaning of the word ‘fruit’ is a structure that contains seeds. Which of these are fruits? Orange; mango; tomato; bean; pod potato. 2. a) Explain what is meant by ‘seed dispersal’. b) Explain why seed dispersal is important for plants. c) List three ways in which fruits can help with seed dispersal. Summary Ovaries develop into fruits after fertilisation. Fruits contain seeds. Fruits have adaptations to help the seeds inside them disperse to new places. Seed dispersal helps to avoid competition with the parent plant. Homework 1.1 a) Copy and complete the word equation for photosynthesis. carbon dioxide +........................... →.............................. +.............................. b) Explain how chlorophyll helps this reaction to happen. Homework 1.2 Carri tested a leaf for starch. The list of steps shows what she did, but they are in the wrong order. a. Put iodine solution onto the leaf. b. Put the leaf into hot ethanol. c. Dip the leaf into water to soften it. d. Put the leaf into boiling water for five minutes. a) List the steps in the correct sequence. b) Explain why Carri carried out step D. c) Explain why Carri carried out step B. Homework 1.3 Yousef did an experiment to find out how giving plants different amounts of water affected their growth. Yousef sowed (planted) nine seeds, each in separate pots. He poured 20 cm3 of water into each pot, to encourage the seeds to germinate. He left all the pots in the same place in the lab. When all the seeds had germinated, Yousef separated the pots into three groups, with three pots in each group. Each day, for seven days, he added a measured volume of water to each pot. Homework Yousef measured the height of each seedling on day 1 and day 7. These are his results. Homework a) Calculate the increase in height for each of the seedlings 7, 8 and 9. b) Calculate the mean increase in height for each group of seedlings. c) On graph paper, draw a bar chart to show Yousef ’s results. Put volume of water on the x-axis, and mean increase in height on the y-axis. d) Write a conclusion that Yousef could make from his results. Homework 1.4 The diagram shows a flower. a) Name the parts labelled A and B. b) Give the letter of the part that attracts insects to the flower. c) Explain why it is useful to the plant to attract insects to its flowers. d) Give the letter of the part of the flower that will develop into a seed. Homework 1.5 The photograph shows a fruit which has been cut in half. a) Explain how you can tell that this is a fruit. b) Name the part of a flower from which a fruit develops. c) Suggest how this fruit helps the seeds to be dispersed. Explain your answer. d) Explain why it is important for seeds to be dispersed.