Biology Revision - Chapter 2

Chemosysnthesis

Carbon dioxide + water + oxygen + hydrogen sulfide -> glucose + sulphuric acid

Vein

Contains tubes called Xylem and Pholem. It also acts has protection for these tubes. Is flexible. To allow it to easily bend to the shape the leaf has been bent without breaking.

Making food

Green plants use water from the environment and carbon dioxide from the air to make the sugar glucose. Light from the Sun provides the energy needed for the reaction. This process is called photosynthesis. The reaction also produces oxygen, which is released into the air during the daytime. Carbon dioxide + water -> glucose + oxygen. The plant uses the glucose for new growth and respiration and also stores unused glucose as a carbohydrate called starch.

Observing stomata

Guard cells have chloroplasts and can photosynthesise. When the guard cells are full of water, they open the stomata. As the plant takes in carbon dioxide (CO2) from the air, oxygen (O2), a waste product of photosynthesis, is removed through the stomata. At the same time, water escapes from the plant. A stoma cannot stay open because the guard cells shrink back as the water escapes, and so the stoma closes.

Chemosynthesis

Is the equivalent of photosynthesis however releases sulfuric acid instead of oxygen and is used where sun light does not penetrate

The importance of green leaves

Leaves have the green colour because they contain chloropyll that absorbs the lights energy within the chloroplast, scientists use chromatography to look at the chemicals in the pigment

Evaluating leaf adatations

Light passes through the cuticle and epidermis until it reaches the palisade cells. The palisade cells absorb as much light as possible, to ensure that the rate of photosynthesis is as high as possible. The spongy cells capture the remaining light. Their surface area and the air spaces allow gases to diffuse through the leaf.

Lower Epidermis

Lower Epidermis is a long cell and has hundreds of tiny holes containing stomata. These holes allow gases to enter and leave the plant. Has hundreds of tiny holes. This allows the plant to get rid of waste products and to absorb gases.

Keeping the water

Plants can lose water from the leaves through the stomata, which let in carbon dioxide. Stomata close in hot conditions. The loss of water from a leaf is called transpiration. Plants lose most water when it is dry, hot and windy. Leaves have a waxy cuticle to prevent water loss. The cuticles of desert plants are much thicker and waxier compared to other plants. Their leaves are often small or needle-like, which also prevents too much water loss. Some plants have curled or folded leaves. The curl reduces the surface area of the leaf. It also traps moist air to help reduce transpiration further.

Stomata

Stoma is the tiny pores in the epidermis of the leaf of a plant, forming a hole of variable width which allows movement of gases in and out of the spaces. Is the holes this allows gases to both enter and leave the plant.

Factors affecting photosynthesis

The concentration of carbon dioxide effects photosynthesis. The more carbon dioxide and water the greater amount of photosynthesis. The chlorophyll in the chloroplast absorbs the energy from the light, therefore the more choloplasts the leaves have the more light it can absorb to carry out photosynthesis

Cuticle

The cuticle is much like our skin, it is a water proof protection, covering the epidermis and other plants of the cell, and limiting water loss. It consists of a waxy-water repellent substance. It has a waxy surface. This allows it to protect the plant and to also stop water from absorbing into the plant.

Palisade

The palisade layer is a layer of parallel elongated cells below the epidermis. This contains most of the chloroplast and most photosynthesis takes place here. The palisade layer is close to the surface of the leaf and contains most of the chloroplasts. This allows it to absorb as much light as possible

Spongy layer

The spongy layer consists of rounded cells which has gas spaces I between them. Gas exchanges occur here It has rounded cells. This allows there to be space in between the cells to allow gas exchanges.

Xylem

The tube inside the vein that contain water and salt to be carried around the plant. A thin tube. To allow food to travel to different parts of the plant

Pholem

The tube inside the vein that takes away dissolved food. A thin tube to allow food to be taken away

Upper Epidermis

The upper epidermis is a thin layer of single sells, which is transparent, containing no chloroplast and allows light to go straight through it. It is transparent and thin, with no chloroplasts. To allow more light to reach the palisade cells.

Looking at the cells

Water and minerals move from the roots up the plant, in a series of cells in the stem. These xylem cells form a pipeline through the plant. The roots of the plant have special cells called root hair cells. These have long, hair-like extensions that penetrate between the soil particles. They have a large surface area through which they can absorb water. The guard cells are also important for controlling water loss (see Topic 2.5). When the guard cells are swollen with water, they open the stomata to let excess water leave the leaf. When the guard cells contain little water, they close the stomata.

Use of plants

We use plants mainly for removing carbon dioxide from the atmosphere and then releasing oxygen

Essential minerals

When plants photosynthesise, they make glucose from carbon, hydrogen and oxygen. To convert these to protein, the element nitrogen must be added. Most plants obtain their nitrogen from the soil in the form of nitrates. Minerals are needed to make proteins, chlorophyll and energy-storage molecules. Not all minerals have the same importance for the plant. The major minerals that plants use in large quantities are called 'macroelements'. Phosphorous, potassium and nitrogen are the main macroelements. Others are sulfur, calcium and magnesium.

Checking the evidence

You can show that a plant has photosynthesised by testing its leaves for starch. This is done using a chemical called iodine. Iodine is an orange colour, but it turns blue-black when added to starch. First, the leaf needs to be boiled in ethanol and then rinsed in warm water. This kills the cells and removes the green colour. Iodine is then added. If the leaf become blue-black, then starch is present, showing that photosynthesis has taken place.