ADDITIONAL SCIENCE (Biology | Cells)

Nucleus - Contains genetic material, which controls the activities of the cell.

Cytoplasm - Most chemical processes take place here, controlled by enzymes.

Cell Membrane - Controls the movement of substances into and out of the cell.

Mitochondria - Most energy is released by respiration here.

Ribosomes - Protein synthesis happens here.

Cell Wall - Strengthens the cell.

Chloroplasts - Contains Chlorophyll, which absorbs light energy for photosynthesis.

Permanent Vacuole - Filled with cell sap to help keep the cell turgid.

Cells may be specialized for a particular function. Their structure will allow them to carry this function out. Here are some examples:

Leaf Cell: It's function is to absorb light energy for photosynthesis. It's adaption is that it's packed with chloroplasts, regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.

Root Hair Cell: It's function is to absorb water and mineral ions from the soil. It's adaption is that it has a long finger like process with a very thin wall, which gives it a large surface area.

Sperm Cell: It's function is to fertilize an egg cell. (Female Gamete). It's adaption is that the head contains genetic information and an enzyme to help penetrate the egg cell membrane. The middle section is packed with mitochondria for energy. The tail moves the sperm to the egg.

Red Blood Cells: It's function is that it contains haemoglobin to carry oxygen to the cells. It's adaption is that the thin outer membrane lets oxygen diffuse easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.

Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.

Diffusion: The movement of particles (molecules or ions) from an area of higher concentration to an area of low concentration.

Diffusion occurs when particles spread. They move from a reigon where they are in high concentration to a reigon where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in soloutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration.

Water can also move across cell membranes because of osmosis. For osmosis to happen you need

- Two soloutions with different concentrations

- A partially permeable membrane to separate them

Partially permeable membranes let some substances pass through them, but not others. Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

Osmosis is important to plants. They gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them turgid or stiff so they that able to hold the plant upright.