The nature and variety of living organisms

Question 1

What is MRS GREN?

Answer 1

M = MOVEMENT
Living things are able to
move about.
Animals move from one
place to another.
Plants move by
responding to light

R = RESPIRATION
Living things need
energy to carry out
the cellular processes
to keep them alive.

S = SENSITIVITY
Living things notice and
react to changes in
their surroundings. They
can respond to light, heat,
sound, taste, sight or
touch.

G = GROWTH
Living things grow
by increasing in size
and complexity

R = REPRODUCTION
Living things produce
offspring.

E = EXCRETION
Living things get rid of
unwanted waste products.

N = NUTRITION
Food to survive

Question 2

What is a cell?

Answer 2

A smallest unit of a living organism.
During development, cell can differentiate to form specialised cells.

Question 3

UNICELLULAR ORGANISMS

Answer 3

A single cell

Examples: Bacteria.

They can perform life functions
such as metabolism, reproduction,
transport of materials.

Question 4

MULTICELLULAR ORGANISMS.

Answer 4

They are made of multiple cells.

Examples: animals and plant cells

Question 5

Eukaryotes: Animal cells

Answer 5

*They are multicellular organisms.
* They do not have chloroplasts because
they do not carry photosynthesis.
* They do not have cell walls.
Examples include:
* Mammals (e.g. humans)
* Insects (e.g. mosquito)

Question 6

Eukaryotes: Animal cell

Answer 6

Question 7

Eukaryotes: Plant cell

Answer 7

They are multicellular organisms.
* They have the same organelles as
the plant cells but have additional
ones:
o Chloroplasts
o Cell wall
o Permanent vacuole
Examples include:
* Flowers
* Cereal e.g. maize
* Herbaceous vegetables e.g. peas

Question 8

Eukaryotes: Fungi

Answer 8

They are vary in shape and have similar
structure to plant cells but do not have
chloroplasts.
*They spread by tiny spores
e.g. seeds via wind and rain to make new
fungus seeds.
* They are more complex and large than
bacteria.
* They live in warm and moist locations.
* Some fungi can be seen with the naked
eye.
* Other fungi are made from unicellular
cells e.g. yeast

Question 9

Eukaryotes: Plant cells

Answer 9

Organelle Function
Permanent
Vacuole
Large space containing cell sap.
It stores carbohydrates e.g. starch, sucrose
It helps keep the cell rigid.
Cell Wall It is made of cellulose and forms a rigid barrier to
strengthen and support the cell.
Chloroplast
It contains a green pigment called chlorophyll.
It absorbs light energy from the sun to make their food
(glucose) by photosynthesis.

Question 10

Eukaryotes: Protists

Answer 10

They are microscopic single-celled
organisms.
For example:
Amoeba: They have similar
organelles to animal cell and live in
pond water.
Chlorella: they have similar structure
to plants and have chloroplasts.

Question 11

Eukaryotes: Protist

Answer 11

Question 12

Prokaryotes

Answer 12

• They are unicellular organisms (single-cell).
• They are arranged to different shapes and sizes.
• They are simple and small single cells with a free,
  loose nucleus. They do not have a nucleus.
• They rapidly reproduce
• Most are in the range of 0.5 – 2 micrometres.
• They lack organelles.
• They can produce toxins and damage the cell.
• They can live everywhere and survive very high
  or very low temperatures.

Question 13

Prokaryotes: Bacteria

Answer 13

Bacteria have the following structures:
* cell wall, cell membrane, ribosomes, cytoplasm.
* Some bacteria can carry out photosynthesis but most rely on other
living or dead organisms.
* They have additional structures.
Organelle Function
Flagella long, thread-like protein structures for movement.
Pili Sticky projections
Capsule Some bacteria have a sticky and slimy capsule outside the cell wall
for adherence.
Plasmid Some bacteria have plasmids which are circular DNA molecules
that can transfer DNA to other cells and can cause antibiotic
resistance.

Question 14

Prokaryotes: Bacterias

Answer 14

Some bacteria cause food poisoning
due to undercooked food e.g.a rodshaped bacterium salmonella.
* Pneumococcus, a spherical bacterium
that acts as the pathogen causing
pneumonia.
* Some bacteria can be used to make
yoghurt and cheese e.g. lactobacillus –
a rod-shaped bacterium.
* Others can be used to make medicine.

Question 15

Viruses

Answer 15

These are not living organisms.

They 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:
- the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts

• the influenza virus that causes ‘flu’
• the HIV virus that causes AIDS.