GCSE Biology: The Feeding of green plants

Plants make their own food by using inorganic substanced to build up organic substances. e.g. using carbon dioxide, water and minerals to produce glucose/starch (carbohydrates) fats and proteins. Making your own food means you are autotrophic. Plants can only make their own food with the presence of chlorophyll found in chloroplasts. The energy thei require for photosynthesis is from the sun as light energy. It is the chlorophyll molecule in the plant that gives it its green pigment. Chlorophyll traps/absorbs light energy. It later releases it so that it will make the carbon dioxide and water combine with the help of the enzymes. All of these processes occur inside the chloroplast. A plant uses carbon dioxide, water and minerals to produce food. a plant uses solar energy (light) from the sun to make carbon dioxide combine with water. Chlorophyll absorbs the sunlight. Chlorophyll is a green pigment stored in the chloroplasts. When sunlight falls on a chlorophyll molecule the energy is absorbes. The chlorophyll molecule releases that energy. A balanced equation means that you have the same amount of reactant before and after the reaction.

The majority of chloroplasts are found in the leaves but they are also present in the stem. Because of this it is important that the leaves are as well adapted as possible in capturing/absorbing light energy and absorbing carbon dioxide from the environment. At the same time the plant does not want to loose too much water through its leaves.

The flat part of the leaf is called a lamina. The stalk that attaches the plant to the leaf is called a petiole. The top and bottom of the leaf are covered with a layer of closely fitting cells called the spidermis. These cells do not contain chloroplasts as their function is to protect the inner leaf, not to photosynthesise. In the lower epidermis there are holes called stomata. They are on the understide so less water escapes via evaporation. at each stomata there are guard cells which open and close. Guard cells do contain chloroplasts.

The missle layer of the plant is called the mesophyll. In the mesophyll there are thick walled xylem vessels for carrying water and smaller vessels called phloem for carrying away food which the leaf has made. This collectively makes up a vein.

The petiole is another name for a leaf stalk. The cells on the upper epidermis made a substance called cuticle which is waxy and stops water evaporating. Stomata are holes in a leaf where gas exchange takes place. Guard cells are a pair of sausage shaped cells that open and close to let in/out gases. Palisade and guard cells in the spongy layer all contain chloroplasts. Those in the upper and lower epidermis do not have chloroplasts.

Carbon Dioxide