B2.1 Cells and Cell Structures
Summary
All living things are made up of cells. The structures of different types of cells are related to their functions. To get into or out of cells, dissolved substances have to cross the cell membranes.
Cells
- Cells are the smallest unit of life.
- All living things are made of cells.
- Most human cells, like most other animal cells, have the following parts: o nucleus
o cytoplasm
o cell membrane o mitochondria o ribosomes
- Plant and algal cells also have:
o cell wall
o chloroplasts
o permanent vacuole
What do these structures do?
- Nucleus – controls the activities of the cell.
- Cytoplasm – where most of the chemical reactions take place.
- Cell membrane – controls the passage of substances in and out of the cell.
- Mitochondria – where most energy is released in respiration.
- Ribosomes – where protein synthesis occurs.
- Cell wall – made of cellulose and strengthens plant cells.
- Chloroplasts – absorb light energy to make food in plant cells.
- Permanent vacuole – filled with cell sap in plant cells.
Yeast
- Yeast is a single-celled organism.
- The cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.
Bacteria
- Bacterium is a single-celled organism.
- A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall.
- The genes are not in a distinct nucleus.
- Cells may be specialised to carry out a particular function. Examples:
Movement into and out of cells
- To get into or out of cells, dissolved substances have to cross the cell membranes.
- Solutes = particles in solution eg glucose, sodium ions, chloride ions.
- Solvent = liquid in which the particles are dissolved eg water.
- Solute and solvent molecules move around randomly.
- Solutes can move into and out of cells by diffusion.
Diffusion
- Diffusion is the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration.
- Oxygen required for respiration passes through cell membranes by diffusion.
- The greater the difference in concentration, the faster the rate of diffusion.
