Biology - Organisation of the Organism

Compare the structure of a plant cell with an animal cell.*

• Both plant and animal cells have a cell membrane, cytoplasm, nucleus, ribosomes and mitochondria.

• Plant cells also have a cellulose cell wall and a large permanent vacuole, and photosynthetic plant cells contain chloroplasts.

• Animal cells do not have a cellulose cell wall or chloroplasts and do not normally have a large permanent vacuole.

Describe the structure of a bacterial cell.

• A bacterial cell has a cell wall, cell membrane, cytoplasm and ribosomes.

• Its main DNA is circular and lies free in the cytoplasm because there is no nucleus.

• Small additional circles of DNA called plasmids may also be present.

• Bacterial cells do not contain mitochondria.

Identify the main structures in plant, animal and bacterial cells.*

• Plant and animal cells: identify the cell membrane, cytoplasm, nucleus, ribosomes and mitochondria; in plant cells also identify the cellulose cell wall, chloroplasts and large permanent vacuole where present.

• Bacterial cells: identify the cell wall, cell membrane, cytoplasm, ribosomes, circular DNA and plasmids.

State the functions of the main structures in plant, animal and bacterial cells. *

• Cell membrane: controls movement of substances into and out of the cell.

• Cytoplasm: site of many chemical reactions.

• Nucleus: contains DNA in chromosomes.

• Cell wall: supports the cell.

• Ribosomes: site of protein synthesis.

• Mitochondria: site of aerobic respiration and energy release.

• Chloroplasts: site of photosynthesis.

• Vacuole: contains cell sap and helps maintain turgor in plant cells.

• Circular DNA: main bacterial genetic material.

• Plasmids: small additional circles of bacterial DNA.

How are new cells produced?

• New cells are produced by division of existing cells.

State the functions of the specialised cells named in the syllabus.

• Ciliated cells: their cilia waft mucus containing trapped particles and pathogens along the trachea and bronchi, away from the lungs.

• Root hair cells: absorb water and mineral ions from the soil.

• Palisade mesophyll cells: absorb light and carry out photosynthesis.

• Neurones: transmit electrical impulses from one part of the body to another.

• Red blood cells: transport oxygen using haemoglobin.

• Sperm cells and egg cells: gametes whose nuclei fuse during fertilisation; sperm cells are adapted to reach the egg cell.

Define cell, tissue, organ, organ system and organism.

• Cell: the basic structural unit of an organism.

• Tissue: a group of similar cells working together.

• Organ: a structure made of different tissues working together.

• Organ system: a group of organs working together.

• Organism: an individual living thing.

State the formula for magnification.

• magnification = image size ÷ actual size

How do you calculate magnification, image size and actual size?

• Magnification = image size ÷ actual size.

• Image size = magnification x actual size.

• Actual size = image size ÷ magnification.

• Make sure image size and actual size are in the same units before calculating.

How do you convert between millimetres (mm) and micrometres (um)?

• 1 millimetre (mm) = 1000 micrometres (um).

• To convert mm to um, multiply by 1000.

• To convert um to mm, divide by 1000.