Biology Cells

All animals and plants are made of cells. Animal cells and plant cells have features in common, such as a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, and often have chloroplasts and a permanent vacuole. Note that cells may be specialised to carry out a particular function. Function of cells which animal and plant cells have in common-

Part-Nucleus: Contains genetic material, which controls the activites of the cell.

 Part- Cytoplasm: Most chemical processes take place here, controlled by enzymes. Part- Cell membrane: Controls the movement into and out of the cell.

Part- Mitochondria: Most energyis released by respiration here.

Part- Ribosomes: Protein synthesis happens here

Part: Cell wall: Helps stengthen the cell

Part: Chloroplasts: Contains chlorophyll, which absorbs light energy for photosynthesis.

Part: Permanent vacuole: Filled with cell sap, to help keep the cell turgid ( having a turgor, enlarged and swollen with water.

Cells may be specialised for a particicular function. Their structure will allow to carry out this function

Leaf cell: Function: Absorbs light energy for phtosynthesis. Adaption: Packed with chloroplasts. Regular shaped , closely packed cells from continuous layer for efficent asorbtion of sunlight.

Root hair cell: Function: Absorbs water and mineral ions from the soil. Adaption: Longer 'finger like', with very thin wall, which gives a very large surface area.

Red blood cells: Function: Contain haemoglobin to carry out oxygen to the cells. Adaption: Thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficently. No nucleus, so the whole cell is haemoglobin.

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

Definition of diffusion: The movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration.

Diffusion occurs when particles want to spread.They move from one region where they in high concentration to a region where they are low in concentration. Diffusion happens when particles are free to move. This is true is gases and for particles dissolved in solutiions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen.

Definition of concentration gradient: A difference between two areas next to each other. Particles will move down the concentration gradient to an area of high concentration to an area of low concentration.

Water can move across cell membranes due to osmosis. For osmosis to happen you will need: Two solutions with different concentrations and a partially permeable membrane to separate them. Partially permeable membranes let some substances through them but not others.

Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through partially permeable membrane.

Eventually the level on the more concentrated side of the membrane rises, while on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net of water is zero and their is no further change in the liquid levels.

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