DEFINITIONS - Topic 1 – The Nature and Variety of Living Organisms

Amoeba

Protoctists that live in pond water and resemble animal cells.

Cell

The basic building block of all living organisms.

Cell membrane

A partially permeable barrier that surrounds the cell.

Cell wall

An outer, structural layer that surrounds some cells. In plant cells, it is made of cellulose. In fungi, it is made of chitin.

Chlorella

A protoctist that has features similar to plant cells e.g. chloroplasts.

Chloroplast

An organelle which is the site of photosynthesis.

DNA

A double-stranded polymer wound to form a double helix. It carries the genetic code.

Eukaryotic cell

A type of cell found in plants and animals that contains a nucleus.

Human Immunodeficiency Virus (HIV)

An infectious virus that weakens the immune system and can lead to AIDS (acquired immunodeficiency syndrome).

Hyphae

Long filaments of a fungus that contain many nuclei.

Influenza virus

An infection virus that causes influenza (the flu).

Lactobacillus bulgaricus

A rod-shaped species of bacterium used to produce yoghurt

from milk.

Mucor

A multicellular fungus that has a hyphal structure.

Mycelium

A collection of thread-like hyphae in a fungus

Pathogens

Microorganisms that cause infectious disease.

Photosynthesis

An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.

Plasmids

Loops of DNA found in the cytoplasm of prokaryotic cells.

Plasmodium

Pathogenic protoctists that cause malaria.

Pneumococcus

A spherical, pathogenic bacterium that causes pneumonia.

Prokaryotic cell

A type of cell found in bacteria that does not contain a nucleus.

Protoctists

Microscopic single-celled organisms

Saprotrophic nutrition

The mode of extracellular nutrition in which digestive enzymes are secreted onto the food outside the cell and the products of digestion are absorbed.

Tobacco Mosaic Virus (TMV)

A widespread plant pathogen affecting many species of plants which produces a mosaic pattern on the leaves. It infects chloroplasts and limits plant growth.

Virus

A non-living organism that can only reproduce inside host cells. Viruses have no cells, but possess a protein coat containing nucleic acids (DNA or RNA).

Yeast

A single-celled fungus