Animal and Plant Cells

Animal and plant cells

Part Function
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

Extra parts of plant cells
Part Function
Cell wall Strengthens the cell
Chloroplasts Contain chlorophyll, which absorbs light energy for photosynthesis
Permanent vacuole Filled with cell sap to help keep the cell turgid

Bacterial Cells
A bacterium is a single-celled organism. A bacterial cell has a different structure to an animal or plant cell. It has cytoplasm, a membrane and a surrounding cell wall, but the genetic material in a bacterial cell is not in a distinct nucleus.
Yeast Cells
Yeast is a single-celled organism. Like bacterial cells, yeast cells have cytoplasm and a membrane surrounded by a cell wall. But unlike bacterial cells, yeast cells have a nucleus.
Specialised cells
Cells may be specialised for a particular function. Their structure will allow them to carry this function out. Here are some examples:
Examples of the functions of cells
Cell Function Adaption Leaf cell Absorbs light energy for photosynthesis Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight. Root hair cell Absorbs water and mineral ions from the soil Long 'finger-like' process with very thin wall, which gives a large surface area. Sperm cell Fertilises an egg cell - female gamete 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 Contains haemoglobin to carry oxygen to the cells. Thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.

Diffusion
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 occurs when particles spread. They move from a region where they are in high concentration to a region 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 solutions. 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, for example.

Examples of diffusion
Two examples of diffusion down concentration gradients
Location Particles move From To
Gut Digested food products Gut cavity Blood in capillary of villus
Lungs Oxygen Alveolar air space Blood circulating around the lungs
Remember, particles continue to move from a high to a low concentration while there is a concentration gradient.
In the lungs, the blood will continue to take in oxygen from the alveolar air spaces provided the concentration of oxygen there is greater than in the blood. Oxygen diffuses across the alveolar walls into the blood, and the circulation takes the oxygen-rich blood away.
Photosynthesis
Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon dioxide with water to make a sugar called glucose. The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product.
This process is called photosynthesis. Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.
Photosynthesis summary
Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.
During photosynthesis:
• Light energy is absorbed by chlorophyll, a green substance found inchloroplasts in some plant cells and algae
• Absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
• Oxygen is released as a by-product
This equation summarises what happens in photosynthesis: Some glucose is used for respiration, while some is converted into insolublestarch for storage. The stored starch can later be turned back into glucose and used in respiration.
Storage and use of glucose
The glucose produced in photosynthesis may be used in various ways by plants and algae.
Storage
Glucose is needed by cells for respiration. However, it is not produced at night when it is too dark for photosynthesis to happen. Plants and algae store glucose as insoluble products. These include:
• Starch
• Fats and oils
Use
Some glucose is used for respiration to release energy. Some is used to produce:
• Cellulose - which strengthens the cell wall
• Proteins - such as enzymes and chlorophyll
Plants also need nitrates to make proteins. These are absorbed from the soil as nitrate ions.