Last Updated 26 Feb 2020

Key to the food chain: explore how plants are the basis of all life on earth

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Plants are essential for humans and all living organisms. They are the producers in ecosystem which can turn sunlight into usable energy and provide consumers with energy, food and oxygen. Chemical reactions are running on earth all the time. Photosynthesis is probably the most important chemical reaction on earth involving sunlight, the air we breathe, water and green pigment chlorophyll. All biochemical reactions are occurring in a cells, while water and air is combined sugars are stored, than this energy is released by respiration.

Plants are the basis of all life on earth and a starting point in ecosystem. They provide the main energy source received by sunlight, and convert inorganic compounds into organic ones, whereas heterotrophs are absolutely dependent on plants – autotrophs. Most of the autotrophs are photosynthetic organisms which use sun light for synthesizing sugars and other organic compounds and afterwards use it for cellular respiration, fuel and growth. The primary producers on earth are algae, plants and photosynthetic prokaryotes. In the next food chain level are heterotrophs, organisms that directly or indirectly depend on primary producers. Herbivores which consume plants and other primary producers are called primary consumers. Carnivores consuming herbivores are secondary consumers and carnivores that consume carnivores are tertiary consumers. The last group is decomposers. These consumers get their energy from detritus as these matters are organic material such as dead organisms, fallen leaves and wood. They have a secrete enzyme that digest these breakdown products into inorganic compounds where primary producers can use these compounds for their sustenance. Here is an end of ecosystem’s chemical cycling, which shows that we need all of these life organisms in order to function properly and keeping energy flow in ecosystem.

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The food chain requires a lot of photosynthesis. This is a process of plants capturing the sunlight and making carbohydrates and releasing by-product oxygen from carbon dioxide and water. Carbohydrates are perfect source of energy for the body, they are breaking down into sugars as glucose which is more readily to use for our bodies. Overall process is summarized in this word equation: carbon dioxide + water light energy glucose + oxygen. The environment which is essential for photosynthesis to take place is sunlight energy, carbon dioxide which we get from atmosphere and water from the soil. The place where photosynthesis process takes place is in plant leaves organelles, called chloroplasts. It contains important pigment, light sensitive chlorophyll which is responsible for the production of food. It absorbs blue and red light and reflects green light, so that’s why so much of the earth looks green. There are two stages of photosynthesis: light reactions and Calvin cycle. In chloroplast there are stacks of membrane vesicles- thylakoids which contains pigment chlorophyll. Thylakoids are the first place where light energy is converted into chemical energy. When light energy is captured by pigment chlorophyll, then this energy is used to break water molecules into oxygen and hydrogen. The oxygen gasses are diffused to atmosphere threw microscopic pores stomata, where these gasses are used for oxygen- dependent organisms. The hydrogen molecules are further breaking down into electrons and protons and then NADPH is formulated from proteins which are delivered by electrons through thylacoid membrane to NDP molecule. NADP is a vitamin made part of niacin and function as an energy carrying molecule. Forming ion gradient hydrogen ions are building into interior space of thylakoids and this is way of storing energy. This energy is used for synthesis the energy- rich molecule ATP, which is used for all its biological activities.

The second photosynthesis stage is Calvin cycle. The cycle starts by assimilating carbon from atmosphere into organic molecules. This transformation of organic compounds is called carbon fixation. Additional electrons are added to the fixed carbon which is formed then to glucose. This reduction power is provided by NADPH molecule, which was formed in a light reaction. Conversion of carbon dioxide to glucose is required chemical energy, where ATP was formed. Therefore the process making sugars occurs in Calvin cycle, but with a help of ATP and NADPH produced in a light reactions. Glucose is an instant source of energy, and can be converted into other carbohydrates such as sucrose, starch or fructose for long-term energy storage. The majority of food that we eat comes from plants, for example the most storage of starch is found in potatoes and cereal grains. Seeds like corn, nuts use oils as a storage product.

Energy is needed for all living organisms, to maintain reproduction, growth and other cells activities. We get energy from foods we consume and glucose is an instant energy, which is first used by cell. The next essential process is respiration. It is a chemical process which takes place in a cell and must not be confused with breathing. Aerobic respiration which needs oxygen and is combined with food is called oxidation. Food molecules consist of hydrogen, oxygen and carbon atoms. The oxidation process converts carbon to carbon dioxide and hydrogen to water and release the energy whereas cell can use it for other cellular reactions. Aerobic respiration word equation: glucose + oxygenenzymescarbon dioxide + water + energy. Oxidation takes in a series of small steps, because energy is not released all at once, it needs its own enzyme and at every stage a little energy is released. Moreover energy used for this process is always ends as a heat and radiates back into space.

Photosynthesis and respiration is a circulation of chemical reactions in biosphere, without these processes life wouldn’t exist.


1. James E. Bidlack, Shelley H. Jansky,(2011), Stern’s Introductory Plant Biology, Edition twelve, New York, McGraw-Hill.

2. D.G.Mackean, (2002), GCSE Biology, Third edition, London, John Murray (Publisher) Ltd.

3. Campbell Reece, Urry Cain Wasserman, Minorsky Jackson, (2008), Biology, Eight edition, San Francisco, Pearson Benjamin Cummings.

4. Eli C. Minkoff, Pamela J. Baker, (1996), Biology today: An issues approach, United States of America,The McGraw-Hill Companies.

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