1.3) Features of organisms
All living organisms have certain features in common, including the presence of cytoplasm, cell membranes, DNA as genetic material. Also contain ribosomes (in the cytoplasm), floating freely or attached to membranes called rough endoplasmic reticulum. Ribosomes are responsible for protein synthesis and enzymes involved in respiration
The Whittaker five kingdom scheme: Animal, Plant, Fungus, Prokaryote and Protoctist.
The plant kingdom:
- Cell wall made up of cellulose
- Contains chloroplasts with photosynthetic pigments
- Make their own food by photosynthesis
- Produces gametes but no seeds
- Divided into two subclasses: Monocotyledon and Dicotyledon
The animal kingdom:
- Multicellular organisms
- No cell wall or chloroplasts
- Coelenterates, Flatworms, Nematode worms, Annelids, Arthropods, Molluscs, Echinoderms, Vertebrates.
- Vertebrates are animals which have a vertebral column called the spinal column or just the spine and consists of a chain of cylindrical bones joined end to end.
- Poikilothermic (variable temperature) cold blooded.
- Homoiothermic (constant temperature) warm blooded.
The fungi kingdom:
- Made up of thread-like hyphae, rather than cells.
- Many nuclei distributed throughout the cytoplasm in their hyphae.
- Mushrooms, toadstools, puffballs, bracket fungi that grow on tree trunks.
- Mould fungi which grow on stale bread, cheese, fruit or other food.
- The yeasts are single-celled fungi.
The prokaryote kingdom:
- Bacteria and blue-green algae.
- Consist of single cells.
- Different to other single-cell organisms because their chromosomes are not organised into a nucleus.
- Bacteria are very small organisms.
- Cell walls are made, of cellulose, but of a complex mixture of proteins, sugars and lipids.
- Some bacteria have a slime capsule outside their cell wall.
- Cytoplasm may contain granules of glycogen, lipid and other food reserves .
- Each bacterial cell contains a single chromosome, consisting of a circular strand of DNA.
- The chromosome is not enclosed in a nuclear membrane but is coiled up to occupy part of the cell.
- Flagella can flick and move the cell about.
The protoctist kingdom:
- Single-celled (unicellular) organisms
- Their chromosomes enclosed in a nuclear membrane to form a nucleus.
- Euglena, possess chloroplasts and make their food by photosynthesis. Often referred to as unicellular ‘plants’ or
- Amoeba and Paramecium, take in and digest solid food. May be called unicellular ‘animals’ or
- Have a central core of RNA or DNA surrounded by a protein coat.
- No nucleus, cytoplasm, cell organelles or cell membrane.
- Virus particles therefore are not cells.
- Do not feed, respire, excrete or grow.
- Do reproduce, but only inside the cells of living organisms, using materials provided by the host cell.
- The nucleic acid core is a coiled single strand of RNA.
- The coat is made up of regularly packed protein units called capsomeres each containing many protein molecules.
- The protein coat is called a capsid.