Biology Revision Cards - Cell activity

Animal cells have:

• Nucleus - controls all activities of the cell and contains the genes

• Cytoplasm - a liquid gel in which most of the chemical reactions take place

• Cell membrane - controls the passage of substances in and out of the cell, e.g lets glucose and mineral ions into the cell and lets out urea and hormones

• Mitochondria - where oxygen is used and most of the energy is released during respiration

• Ribosomes - where protein synthesis takes places

Plant cells have:

• Nucleus
• Cytoplasm
• Cell membrane
• Mitochondria
• Ribosomes
• Cell wall - made of cellulose that strengthens the cell and gives it support

Many but not all plant cells have:

• Chloroplasts - found in the green parts of the plant and contain chlorophyll which absorbs light energy to make food by photosynthesis. Root cells do not have chloroplasts because they are underground and do not photosynthesise.

• A permanent vacuole - space in the cytoplasm filled with sap to keep the cells rigid to support the plant.

Flagella - a long protein strand which is used by bacteria to move around.

Bacteria is useful to people because it is used:

• to make foods such as yoghurt and cheese
• in sewage treatment
• to make medicines
• as decomposers in food chains and webs
• in natural cycles such as the carbon and nitrogen cycles

Bacteria is damaging to people because:

• it can cause diseases

Yeast reproduce by asexual reproduction. This involves a a new yeast cell growing out form the original cell to form a separate yeast organism.

- Specialised to survive for a long time, even when there is little oxygen available.

-When yeast cells have plenty of oxygen they use aerobic respiration. They use oxygen to break down sugar to provide energy for the cell. ==> carbon dioxide and water produced as waste products

When they have little oxygen they can use anaerobic respiration. When yeast cells break down sugar in the absence of oxygen ==> ethanol and carbon dioxide produced as waste products.

Used:

• To make bread
• To make alcoholic drinks
• In the production of antibiotics e.g penicillin

If something is specialised it is adapted to suit its function. e.g Root hair cells

- Found close to tips of growing roots, help the plants take up water and mineral ions more efficiently ==> close to the xylem tissue which carries water and mineral ions up into the rest of the plant.

• The root hairs increase the surface area for water to move into the cell
• Has a large permanent vacuole that speeds up the movement of water by osmosis from the soil across the root hair cell.

Diffusion is the spreading of the particles of any substance in solution, or particles of a gas from a region where they are of a high concentration to a region with a lower concentration.

The greater the difference in concentration the faster the rate of diffusion.

Osmosis is the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules.

• Two solutions with the same concentration are isotonic
• If 2 solutions have different concentrations, the more concentrated solution is hypertonic and the more dilute solution is hypotonic.
• If a cell is placed in a solution hypertonic to its cell contents, water will leave the cell. Animal cells shrivel and plant cells plasmolyse (cell membrane and cytoplasm pull away from cell wall).
• If a cell is placed in a solution hypotonic to its cell contents, water will enter the cell. Animal cells swell and burst and plant cells become turgid.

Active transport is when substances are absorbed against a concentration gradient. This requires the use of energy from respiration.

Active transport enables:

• plants to absorb ions from very dilute solutions, e.g by root hair cells

• sugar may be absorbed from low concentrations in the intestine and from low concentration sin the kidney tubules.

There are many adaptations to make the process of exchange more efficient. The effectiveness of an exchange surface area can be increased by:

• Having a large surface area that provides a big area over which exchange can take place
• Being thin, which provides a short diffusion path
• Having an efficient blood supply; this moves the diffusing substances away and maintains a concentration gradient
• Being ventilated to make gaseous exchange more efficient by maintaining steep concentration gradients

Villi - The finger-like projections from the lining of the small intestine which increase the surface area for the absorption of digested food into the blood

D - Has many microvilli: Ex - Provides large surface area

D - Many capillaries: Ex - Maintains concentration diffusion gradient

D - Have a thin wall/ capillaries are near the surface: Ex - Short distance for food to travel

D - Many mitochondria: Ex - provide energy