biology paper 1 revision

biology paper 1 revision

cell structure

nucleus - controls activities of the cell

cytoplasm - where most of the chemical reactions take place

cell membrane - controls what goes in and out of a cell

mitochondria - where most of the energy is released in respiration

ribosomes - where protein synthesis takes place

chloroplasts - absorb light energy to make food

microscopy

Magnification = size of image / size of real object

cell division

chromosomes - The nucleus of a cell contains chromosomes made of coiled DNA molecules, they are the genetic information. Each chromosome carries a large number of genes. In body cells, the chromosomes are normally found in pairs. Models and analogies can be used to develop explanations of how cells divide.

Cells divide into a series of stages called the cell cycle. There are several stages of the cell cycle, including mitosis.

During the cell cycle, the genetic material is doubled and then divided into two identical cells.

Before a cell can divide it needs to grow and increase the number of subcellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome.

In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides.

Finally, the cytoplasm and cell membranes divide to form two identical cells.

Cell division by mitosis is important in the growth and development of a multicellular organism

transport in cells

Osmosis

Dissolved substances move by diffusion and by active transport.

Water often moves across boundaries by osmosis. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules.

Differences in the concentrations of the solutions inside and outside a cell cause the water to move into or out of the cell by osmosis.

Active Transport

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration.

This process enables cells to absorb substances from very dilute solutions.

2 examples:

• Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth.

It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.

the digestive system

The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

The digestive system includes:

• Glands, such as the pancreas and salivary glands, which produce digestive juices

• Stomach and small intestine, where digestion occurs

• Liver, which produces bile

• Small intestine, where the absorption of soluble food occurs

• The large intestine, where water is absorbed from the undigested food, producing faeces.

the heart

The heart is an organ that pumps blood around the body in a double circulatory system. Much of the wall of the heart is made from muscle tissue.

There…