Tag: biology revision notes

Ingestion is the taking of substances such as food and drink into the body through the mouth. Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules. Chemical digestion is the breakdown of large insoluble molecules into small soluble molecules. Absorption is the movement of small food molecules and ions through the wall of the intestine into the blood. Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells. Egestion is the passing out of food that has not been digested or absorbed, as faeces, through the anus.

All living organisms need food. An important difference between plants and animals is that green plants can make food in their leaves but animals have to take it in ‘ready-made’ by eating plants or the bodies of other animals.

The relationship between a leaf and the rest of the plant is described in other topics. A typical leaf of a broad-leaved plant is needed as well as a transverse section through the leaf.) It is attached to the stem by a leaf stalk, which continues into the leaf as a midrib. Branching from the midrib is a network of veins that deliver water and salts to the leaf cells and carry away the food made by them. As well as carrying food and water, the network of veins forms a kind of skeleton that supports the softer tissues of the leaf blade. The leaf blade (or lamina) is broad.

Although the details of photosynthesis vary in different plants, the hypothesis as stated in this chapter has stood up to many years of experimental testing and is universally accepted. The next section describes how photosynthesis takes place in a plant.

Photosynthesis is the process by which plants manufacture carbohydrates from raw materials using energy from light.

A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction. An enzyme is a protein that functions as a biological catalyst.

A DNA molecule is made up of long chains of nucleotides, formed into two strands. A nucleotide is a 5-carbon sugar molecule joined to a phosphate group (–PO3) and an organic base. In DNA the sugar is deoxyribose and the organic base is either adenine (A), thymine (T), cytosine (C) or guanine (G).

The chemical elements that make up carbohydrates, fats and proteins. The sub-units that make up biological molecules Food tests for starch, reducing sugars, proteins, fats and oils, vitamin C. The role of water is of a solvent.

If a dilute solution is separated from a concentrated solution by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution. This is known as osmosis.