Cells, classification and movement into and out of cells

Characteristics of living organisms

Movement, respiration, sensitivity, growth, reproduction, excretion and nutrition (MRS GREN). Classification uses shared features; the binomial system (genus and species, e.g. Homo sapiens); dichotomous keys.

Cell structure

Animal and plant cells (nucleus, cytoplasm, cell membrane, mitochondria, ribosomes; plant cells also have a cellulose cell wall, chloroplasts and a large vacuole); bacterial cells (no nucleus, circular DNA, plasmids). Specialised cells: red blood cells, root hair cells, palisade cells, ciliated cells, sperm and egg cells. Levels of organisation: cell → tissue → organ → organ system → organism.

Magnification

Magnification = image size ÷ actual size.

Movement into and out of cells

• Diffusion: net movement of particles from higher to lower concentration, down a gradient, as a result of random movement.
• Osmosis: net movement of water from a dilute solution (high water potential) to a concentrated solution through a partially permeable membrane. Turgor and plasmolysis in plant cells; animal cells burst or shrink.
• Active transport: movement against a concentration gradient using energy from respiration (ion uptake by root hairs).

Check yourself

1. Write the scientific name of humans in the binomial system.
2. Name the structure in bacteria that carries extra genes.
3. What happens to a plant cell placed in concentrated salt solution?