1. The nature and variety of living organisms

Question 0

describe the common features shared by organisms within the following main groups:

plants
animals
fungi
bacteria
protoctists
viruses

Answer 0

Plants:
Multicellular organisms
Their cells contain chloroplasts- able to carry out photosynthesis
Their cells have cellulose cell walls
They store carbohydrates as starch or sucrose
Examples include flowering plants, such as a cereal (for example maize), and a herbaceous legume (for example peas or beans)

Animals:
These are multicellular organisms
They have no cell walls
They usually have nervous coordination and are able to move from one place to another
They often store carbohydrate as glycogen
Examples include mammals (for example humans) and insects (for example mosquito)

Fungi:
Usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei
Some examples are single-celled
Their cells have walls made of chitin
They feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products (saprotrophic nutrition)
They may store carbohydrate as glycogen
Examples include Mucor (hyphal example) and yeast (single cell example)

Bacteria:
These are microscopic single-celled organisms
They have a cell wall, cell membrane, cytoplasm and plasmids
They lack a nucleus but contain a circular chromosome of DNA
Some bacteria can carry out photosynthesis but most feed off other living or dead organisms
Examples include Lactobacillus bulgaricus (used in the production of yoghurt from milk) and Pneumococcus (pathogen causing pneumonia)

Protoctists:
These are microscopic single-celled organisms
Some, like Amoeba, that live in pond water, have features like an animal cell
Some like Chlorella, have chloroplasts and are more like plants
A pathogenic example is Plasmodium, responsible for causing malaria

Viruses:
These are small particles, smaller than bacteria
They are parasitic and can reproduce only inside living cells
They infect every type of living organism
They have a wide variety of shapes and sizes
They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA
Examples include the tobacco mosaic virus, the influenza virus (causes ‘flu’) and the HIV virus (causes AIDS)

Question 1

What is a ‘pathogen’?

Answer 1

Pathogens are micro-organisms that cause disease.

Bacteria, fungi, viruses and protoctists all cause disease in a variety of ways.

For example, bacteria release toxins. Another useful example of pathogens causing disease is viruses destroying host cells.

Question 2

What characteristics do all living organisms share?

MRS C GREN

Answer 2

M ovement
R espiration
S ensitivity

C ontrol

G rowth
R eproduce
E xcrete
N utrition