bio.txt

Plants make food by photosynthesis. ‘Photo’ means ‘light’. ‘ Synthesis’ means ‘making’. So, photosynthesis means ‘making with light’. In photosynthesis, plants use: water, which they get from the soil carbon dioxide, which they get from the air energy, which they get from sunlight...

Plants make food by photosynthesis. ‘Photo’ means ‘light’. ‘ Synthesis’ means ‘making’. So, photosynthesis means ‘making with light’. In photosynthesis, plants use: water, which they get from the soil carbon dioxide, which they get from the air energy, which they get from sunlight ▪ The energy in sunlight is captured by a green pigment, called chlorophyll, which is inside some of the cells in the leaves of plants. ▪ Photosynthesis happens in the leaves of a plant. How plants make their own food ▪ The plants use the energy to make the water and carbon dioxide combine together in a chemical reaction. ▪ Two new substances are made in the reaction. These are glucose and oxygen. ▪ You can write the word equation for photosynthesis like this: ▪ water + carbon dioxide → glucose + oxygen Keywords photosynthesis: a series of chemical reactions that take place inside the chloroplasts of plants, in which carbon dioxide and water react together using light energy; the products are glucose (and other carbohydrates) and water chlorophyll: a green pigment present in chloroplasts, which absorbs energy from light and helps to transfer it to the carbohydrates made in photosynthesis light intensity: a measure of the quantity of light energy falling onto an object Photosynthesis Respiration Photosynthesis only happens in cells of green plants Respiration happens in all living cells Happens in chloroplasts. Happens in cytoplasm and mitochondria Dependent on light Not dependent on light Oxygen is given out Carbon dioxide is given out Energy from sunlight is stored as chemical energy in glucose. Energy in glucose is released for the cell to use The reactants in respiration are the products in photosynthesis, and vice versa Why is photosynthesis important? Plants use the energy in sunlight to make glucose and other carbohydrates. These carbohydrates contain some of the energy that was originally in the sunlight. When animals eat food, they get some of the energy that was captured by plants. All the energy in all the food in the world comes from plants. (provides glucose for food and energy) A food chain shows us how this energy is passed along from one organism to another. The second reason that photosynthesis is so important is that it provides oxygen for the Earth’s atmosphere. Animals and plants, of course, need oxygen for respiration.Chloroplasts and chlorophyll Chlorophyll essential for photosynthesis. captures energy from sunlight. The energy helps water and carbon dioxide to react together. kept inside chloroplasts, inside plant cells. Photosynthesis happens inside chloroplasts. Not all cells have chloroplasts, so not all plant cells can photosynthesise.On warm, sunny days, plants can make more carbohydrate than they need to use immediately. So they store some it for use later on –at night, or at a time of year when there is less sunlight. Plants store carbohydrates as starch. They store the starch inside the chloroplasts in their cells.Photosynthesis happens inside chloroplasts, which are inside the cells in the middle layers of a leaf. Leaves are very thin, so it is easy for sunlight to reach these cells. Chloroplasts also need plenty of water and carbon dioxide, because these are used in photosynthesis. Water is brought to the cells in the leaf along the veins. Carbon dioxide diffuses into the leaf from the air. If you look at the diagram, you can see that there are tiny holes in the leaf, which allow gases to diffuse in and out. These holes are called stomata (singular: stoma). The gases can easily diffuse through air spaces between the cells inside the leaf.stomata (singular: stoma): a microscopic hole in the surface of a leaf (usually on the underside) through which gases diffuse into and out of the air spaces inside the leaf fertiliser: a substance containing mineral ions required by plants, which can be added to soil yield: the quantity of useful crop obtained at harvest Farmers add fertiliser to their fields because it makes the crops grow larger and produce a higher yield. Yield is the quantity of crop that the farmer harvests. Fertilisers contain minerals. Plants need only quite small quantities of minerals. They get these minerals from the soil, through their roots. But sometimes the soil does not contain enough of certain minerals. This stops the plants growing to their full potential. Magnesium is needed to make the green pigment, chlorophyll. If a plant does not have enough magnesium, its leaves look yellow instead of green. It cannot grow well, because it does not have much chlorophyll to absorb energy from sunlight, and so it cannot photosynthesise as much as it should. Nitrate contains nitrogen atoms. These are needed so that the plant can convert carbohydrates to proteins. Proteins are essential for making new cells, so that the plant can grow well. Without enough nitrogen, leaves die and the plant stays small, like these maize (corn) plants. Nitrogen is also needed to make chlorophyll. Living organisms need carbon. Organisms cannot use carbon in the form of an element. They can only use it when it is part of a compound. Carbon is part of many different compounds that make up cells. Carbohydrates, proteins and fats are all compounds that contain carbon.Plants take carbon dioxide from the air and use it in photosynthesis to make carbohydrates. Carbon dioxide is a compound that contains carbon atoms combined with oxygen atoms. The carbohydrates in plants contain carbon atoms that were originally part of the air. Plants use the carbohydrates to make proteins and fats. All of these nutrients are compounds that contain carbon atoms. We are animals, so we get all of these carbon-containing nutrients when we eat plants or other animals. Decomposers get their carbon when they break down waste products from plants and animals.We can show how carbon gets into the bodies of animals and decomposers using a flow diagram.A lot of carbon dioxide that plants take from the air eventually goes back into the air again. This happens when plants and animal respire. You may remember the respiration equation: glucose + oxygen → carbon dioxide + water + energy All organisms respire. Plants respire all the time. At night, when they cannot photosynthesise, they give out carbon dioxide, just as we do. Decomposers respire, too. As they break down waste products from plants and animals, they release carbon dioxide into the air. When organisms die, they are not always broken down quickly by decomposers. Sometimes, their bodies fall into places where there is no oxygen, such as a peat bog, or deep in the ocean. In these places, the decomposers cannot respire, because there is not enough oxygen for them. Instead, the organisms’ bodies get gradually buried, as more and more sediment builds up on top of them. High pressure and heat change their remains into fossil fuels, including coal, oil or natural gas. Changing dead organisms to fossil fuels takes a very long time. Most of the fossil fuels that we use on Earth today were formed hundreds of millions of years ago.Coal was formed from the remains of plants that grew in huge swamps. Their remains were buried over millions of years, slowly turning into coal. Coal is dug out of the ground and then used in power stations to generate electricity. Fossil fuels contain carbon. When we burn a fossil fuel, the carbon in it combines with oxygen from the air and forms carbon dioxide. This is called combustion.A fossil is the remains of an organism, or traces of it (such as its burrows) that have turned to rock. We can still see the shape of the organism in a fossil. But fossil fuels do not look like organisms at all, and oil and gas are not even rocks. Fossil fuels are given this name because – like fossils – they were formed a very long time ago and buried underground.Weather or climate? When people talk about climate, they mean the weather of a place over a much longer time, usually more than 30 years. Weather can change in a few hours or even in minutes. Climate information includes the statistics of weather information that tells us about the normal weather as well as the range of extreme weather at that place. Climate is the long-term pattern of temperatures, wind and rainfall on Earth.Global warming is a gradual increase in the average temperature on Earth. It is being caused by an increase in ‘greenhouse gases’, which act like a blanket around the Earth. These are gases that can trap heat. Carbon dioxide is a greenhouse gas. Humans burning fossil fuels cause the release of a lot of carbon dioxide.Greenhouse gases Carbon dioxide and methane are ‘greenhouse gases’. In stage 8, you learnt how carbon dioxide helps to keep the Earth warm. Without any carbon dioxide in the atmosphere at all, the Earth would be a frozen place, unable to support life. Greenhouse gases But at the moment, we have too much carbon dioxide in the atmosphere. Look back at the carbon cycle diagram in Topic 1.3. You can see that some carbon from the atmosphere ends up in fossil fuels. But if we extract them and burn them, we release the carbon in them back into the air, in the form of carbon dioxide. Carbon dioxide levels in the atmosphere are increasing. This is affecting the climate on Earth. (causing Global warming)The Earth’s climate has been very different in the past compared to the climate today.Ice Age About 2 billion years ago The first Ice Age Since then Alternate warm (no ice at the poles) & cold (ice age) Snowball Earth 650 million years ago Earth – covered with ice and snow ‘Slushball Earth’ (Slush is melting ice)Asteroids colliding with each other 470 million years ago two asteroids collided with one another between Earth and Mars Collision – produced huge quantities of dust light & heat from Sun another Ice age and the Earth became much colder – the ice caps spread from the poles and sea level fell.Asteroids colliding with Earth 67 million years ago an asteroid collided with Earth near Mexico Collision generated a condition like massive bomb explosion causing a) Very high temperatures near collision site b) Massive tsunami c) Huge amt. of rock and dust less light reaching Earth 9/5/2024 Climate Change 13 Plants can’t photosynthesize No food for animals Disruption of food chains Mass Extinction up to 75% of all the species including dinosaursCould other objects collide with Earth? Objects in space that are smaller than an asteroid are called meteoroids. When meteoroids enter Earth’s atmosphere they are called meteors. Some people call meteors shooting stars as they appear like stars moving very fast across the sky. They usually present little risk as they burn in the atmosphere due to heat from friction. Some large ones can create shockwaves; in 2013 a meteor exploded over Russia and shattered windows. The parts of meteoroids that do collide with Earth are called meteorites.Could other objects collide with Earth? If an object is large enough, it can cause local damage, or even damage that affects the whole planet. In 1998, scientists started making detailed observations of objects that could possibly cause damage to Earth. When assessing the possible risk to Earth, scientists look at: the mass or diameter of the asteroid the closest possible approach to Earth. An asteroid passing further from Earth may be a greater risk than one passing closer if its mass is greater. For example, a comet less than 100 meters across will explode high in the atmosphere and probably do no harm whatsoever. If the comet is 10 kilometers across or larger (that is, if the impact carries an energy of more than about 100 million megatons), the resulting global environmental damage will be so extensive that it will lead to a mass extinction, in which most life forms die. This is what happened 65 million years ago, when the dinosaurs went extinct.slush: partly-melted snow mass extinction: the complete loss of a very large number of species meteoroids: objects in space that are smaller than an asteroid meteors: a meteoroid when it moves through the Earth’s atmosphere meteorite: part of a meteor that reaches the Earth’s surfaceClimate change today and in the future For the last 2000 years or so, our climate has been fairly stable. People living in different places have become used to having more rain at some times of year than at other times, or temperatures that change in a predictable way during one year. Knowing this helps people to choose the best crops to grow, and to know when they should sow seed and collect the harvest. Now, however, the mean temperatures on Earth are increasing. This is caused by an increase in carbon dioxide concentration in the atmosphere. Carbon dioxide is a greenhouse gas, which traps heat energy close to the Earth’s surface. When carbon dioxide concentrations increase, more heat is trapped. The higher temperatures mean that there is more energy in the atmosphere. This increases the chance of extreme weather events, such as hurricanes and typhoons. Many scientists think that we are already seeing an increase in the number of storms, and in their severity. It is difficult to be certain, because there has always been a lot of variation each year in the number of big storms. Tropical cyclone Idai hit the east coast of southern Africa in 2019. It was one of the worst storms ever to affect Africa and killed more than 1300 people. Severe flooding destroyed homes and fields, damaging people’s livelihoods. Was this a result of climate change? We cannot say, because storms like this can happen anyway. However, there seem to be more of them now, and they are more violent. The changing climate is also making it more difficult for people in some parts of the world to grow crops. Rains may come late, or might not come at all. Or rain may fall when it doesn’t normally fall – or fall much more heavily, causing flooding. Monsoon rains are usually welcomed, but not when they are so heavy that they cause severe flooding. In 2019, the monsoon rains in Pakistan, India, Nepal and Bangladesh came later and were heavier than usual. Millions of people in these countries were affected by floods. When rains fail, people may lose their harvests. Long droughts also increase the risk of wildfires. All of these changes affect not only people, but also plants and animals. This wildfire in Australia followed a long period of drought. The increase in the Earth’s mean temperature affects sea level. Water expands as it is heated, so if the sea temperature increases, sea level rises. Melting ice caps and glaciers add extra water to the oceans. This glacier is getting smaller (retreating) as temperatures increase. Sea level has been rising at a rate of about 3 mm per year. Scientists estimate that more than 600 million people are at risk from flooding caused by sea level rise by the end of this century. Many megacities are built on the coast – such as Shanghai, Mumbai and Los Angeles – and these are especially vulnerable to sea level rise. Water as a Temperature Buffer Water as a Metabolite Water as Living EnvironmentWater as a Solvent Water attracts both positive and negative ions, because of the nature of the chemical bonds in water. Thus, positive ions are attracted to the oxygen in water, while negative ions are attracted to the hydrogen. This allows water to dissolve compounds important for survival, such as glucose gleaned from ingesting food. Water as a Temperature Buffer Water has a high specific heat capacity, meaning it takes a lot of heat to raise its temperature. Thus, water absorbs much heat without the temperature of the organism being raised. This prevents enzymes from becoming overheated and failing to function. Water as a Metabolite The sum total of chemical reactions within an organism is called metabolism. Water is a metabolite, or a chemical involved in reactions. In this way, it is is necessary for the continued survival of both plants and animals. In plants, water aids in photosynthesis. During the process, water splits into hydrogen and oxygen atoms. Oxygen is released into the atmosphere, while hydrogen is used in the rest of the chemical reaction to produce glucose to feed the plant. Water as Living Environment Water-based organisms such as fish require water to breathe, directly breathing the oxygen dissolved in water. Without a water supply, they could not access oxygen and would suffocate.ROOT HAIRS specialised cells in the outer layer of a plant root increase the surface area through which water and mineral ions can be absorbed from the soilHOW ROOT HAIRS ABSORB WATER Plants, like all living things, are made mostly of water. Plants need to absorb water almost all of the time. They do this through their roots. The roots absorb water from the soil. Soil is made up of tiny particles of rock. There are spaces between them, which are filled with air and water. Root hairs grow out of the surface of roots. Root hair cells provide a really big surface through which water and mineral ions can be absorbed into the plant.HOW ROOT HAIRS ABSORB WATER This diagram shows a root hair growing in between soil particles. Each root hair is part of a single cell. Water moves into the root hair cell from the soil. It passes through the cell wall and the cell membrane of the cell, and into the cytoplasm. Mineral ions including nitrate ions and magnesium ions are dissolved in the water between the soil particles, and they move into the root hair cell along with the waterXYLEM VESSELS specialised cells in which all cell contents and end walls have disappeared, leaving an empty tube through which water is transported You can see the root hairs on the outside of the root. In the centre, there are some very special cells called xylem vessels. These are the water transport system of the plant. After water has been absorbed into a root hair cell, it moves from the outside of the root towards the inside. It goes into the xylem vessels in the centre of the root.STRUCTURE OF A XYLEM VESSEL Xylem vessels are long, tube-like cells. They are dead cells – all of their contents, such as cytoplasm and a nucleus, have disappeared. All that is left is their cell walls, with an empty space inside. Their end walls have completely disappeared, too. Many xylem vessels stack on top of one another, making long, empty tubes that reach all the way from the roots, up to the highest parts of the plant.