9D Plants for food 9DPlants for food Food from plants Maximising yield Pests!
9D Plants for food Food from plants
9D What’s on the menu? Do you like your food? Nutrition is one of the life processes. Do these meals come mainly from plants or animals? animal plant animal plant animal plant animal
9D All from plants All of our food comes from plants in some way or other. Only plants can use sunlight energy to make food. What do they need in order to do this? Plants make glucose, which they convert into other chemicals such as starch or cellulose. They make proteins, and they need nitrogen for this. All these chemicals allow the plant to grow.
9D We’ve got a word for that! words biomassnutrients respiration photosynthesis sugar Which word has which meaning? word meaning biomass the mass of an organism, minus the water sugar a sweet, water-soluble carbohydrate respiration a chemical process that releases energy from sugars in cells photosynthesis a chemical process that uses sunlight energy to build sugars from carbon dioxide and water nutrients foods or essential chemicals needed by living things
9D A nice bit of … leaf? Plants make food. But we only eat certain parts of plants. Can you think of a flower that we eat?
9D Yield The mass of the part of a plant that we eat is called the yield. A tomato plant might weigh 7 kg, but the actual tomatoes weigh only 4.5 kg.What does the other 2.5 kg consist of? How can farmers increase the yield of their crops?
9D Plants for food Maximising yield
9D Just a pile of manure If you want to increase plant growth – add fertiliser! In order to grow, plants convert glucose to other chemicals. To make these chemicals they need particular elements.The elements are in minerals in the soil. Can you name three elements that plants need from the soil? Fertilisers provide the right mix of minerals. They make plants healthy, so they grow bigger and give a better yield. Some farmers use organic fertilisers. What does this mean?
9D Match the minerals Without the right mineral elements, plants show deficiency symptoms. minerals nitrogen magnesiumpotassium phosphorus Match the minerals to the symptoms. magnesium potassium nitrogen phosphorus
9D Factors for growth Brian wants to maximise his tomato yield this summer. Are these big, healthy-tomato or small, unhealthy-tomato factors? rain for all of July and August lots of rain but only at night low levels of nitrate in the soil trees cast a shadow over the crop Brian orders a load of manure a sudden aphid attack weeds grow between the plants sunny days
9D Lead nitrate, breakfast of champions? Lead compounds are very poisonous.They are dangerous for plants as well as animals.They may be found in the soil near old mine workings. Some areas of old industrial land are so toxic that very few plants grow there. How do the lead compounds get into the plants to poison them? A class of students tried the following experiment to find out how dangerous lead nitrate solution is to germinating seeds.
9D Setting up the experiment... A B C D E F 1.0 0.1 0.01 0.001 0.0001 0.0 The class used dishes of lead nitrate at different concentrations, and one with deionised water. (The concentrations are in units called mol/dm3.) They put 25 seeds in each dish and left them to grow. Which dish contains pure water? Which dish is 1000 times more concentrated than dish D?
9D After a week... A B C D E F 1.0 0.1 0.01 0.001 0.0001 0.0 This is how the dishes looked after a week. Which solution gave the best growth? Is this surprising? Why?
9D Not so simple A B C D E F 1.0 0.1 0.01 0.001 0.0001 0.0 Plant growth depends on many factors. Can you think of four factors that affect plant growth? Some factors work against each other. The health of a plant depends on the combination of factors. Lead nitrate solution contains poisonous lead. It also contains nitrate, a mineral that plants need.In dishes D and E the positive effect of the nitrate was larger than the negative effect of the lead.
9D Quiz 1.Crop plants grow better in the light than in the shade because… a)they need light for photosynthesis b) they need light for respiration c)it’s easier to see them and look after them. 2.Which of the following has no effect on the crop yield? a)the method of harvesting b) the temperature of the air around the plant c)water levels in the soil.
9D Quiz 3.To increase the yield from a tomato plant you could… a)talk to it b) add fertiliser c)reduce the water supply. 4.The yield of a crop is... a)the mass of the useful part of a plant b) a measure of how easy it is to bend the stalk c)the mass of the total plant.
9D Quiz 5.Growers sometimes pump carbon dioxide into greenhouses to increase the crop yield.This works because… a)it kills insects that eat the plants b) it prevents any fires breaking out c)it increases the rate of photosynthesis. 6.When measuring crop yield it is best to measure... a)dry weight b) fresh weight c)height.
9D Plants for food Pests!
9D What is a pest? words herbicidepersistent pesticide bioaccumulation pest Which word belongs to each definition? pest pesticide herbicide bioaccumulation persistent
9D Bioaccumulation Why does the heron get more poison than the fish? What would happen to a predator that ate the heron?
9D DDT: friend or foe? DDT is a persistent poison. It builds up along the food chain. DDT helps protect crops from locusts. They can eat tonnes of food in a few days. DDT prevents people from starving to death. DDT saves lives! It kills mosquitoes that carry malaria. We all have some DDT inside us now because it persists in the environment. We have poisoned ourselves with this dreadful chemical. DDT has driven some birds of prey almost to extinction. It would have been better if we’d never invented it! DDT – friend or foe? What do you think? And why?
9D To spray or not to spray Aphids (greenfly) are a pest if you grow roses. rosesaphidsladybirdsrobins This is just one of many food chains in a rose-grower’s garden. Which animal is a predator for aphids? Aphids have other predators, including bluetits.Which organism dobluetits compete with?
9D To spray or not to spray You can spray roses with insecticide. The greenfly will go away, but they might come back even worse. Why? You could try biological control. What could you do? Which approach would give you more biodiversity?
9D Biological control To control a pest, you can release a predator to eat it. This biological control has its good points, but it is not perfect. Can you think of some pros and cons? suitable predators are not available for all pests no poisons are left in the environment can be cheaper than chemical pesticides does not remove all the pests, just limits their population safe to use on food crops your predator might get eaten by another animal your predator might get out of control and become a pest itself kills only the pest, not other organisms