Nature and Variety of Living Organisms

edexcel igcse specification (triple science)

saprotrophic nutrition

The term ________ refers to the secretion of extracellular digestive enzymes onto food and then absorbing digested molecules.

prokaryotes

Generally, ________ are smaller than eukaryotes.

Animals

________ consume other organisms to obtain energy, by breaking down complex molecules into simple molecules (which is called digestion)

pathogen

A(n) ________ is any microorganism that causes disease in another organism (e.g.

Plants

________ use sunlight, carbon dioxide and water to produce both oxygen and glucose in photosynthesis.

HIV

________ (Human Immunodeficiency Virus) is a virus that can eventually lead to Acquired Immunodeficiency Syndrome (AIDS)

Fungi

________ are another type of cell.

form of ATP

Energy is transferred in the ________.

Prokaryotic organisms

________ are in a separate kingdom and are different from eukaryotes as they 're always single- celled and don't contain nuclei.

The acronym of MRS H GREN stands for

Movement Respiration Sensitivity Control Growth Reproduction Excretion Nutrition Organisms have to have food to provide energy, which is needed for life processes (movement, respiration and excretion)

There are five kingdoms to classify living organisms

1

Here are the main features of a fungal cell

usually multicellular some can be single-celled made up of thread-like structures (hyphae) hyphae are made of many nuclei and are organised into mycelium cells contain a nucleus with a distinct membrane cells have walls made of chitin cells don't contain chloroplasts

Their main features are

diverse kingdom mainly microscopic and single-celled some aggragte into larger forms contain nucleus with distinct membrane some have features that are more animal-cell like some have features that are more plant-cell like some photosynthesise no nervous coordination For prokaryotic cells, the nuclear material is found in cytoplasm, such as bacteria

examples of pathogens

Bacteria Fungi Protoctists Viruses

They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA Structure of a typical virus Examples of viruses include

The tobacco mosaic virus (TMV) causes discolouring of the leaves on tobacco plants by preventing the formation of chloroplasts The HIV virus causes AIDS The influenza virus causes the ‘flu Tobacco mosaic virus Tobacco mosaic virus (TMV) was the first virus to be isolated by scientists It is a widespread plant pathogen that infects about 150 species of plants including tomato plants and cucumber

movement

can change position

reproduction

can have offspring either sexually or asexually

sensitivity

can detect stimuli, such as light, and respond to them

Control

can control their internal environment (homeostasis)

growth

can increase mass

respiration

can produce energy either aerobically or anaerobically

excretion

can remove toxic or waste produced produced by reactions in the body

nutrition

can absorb nutrients in order to use them for growth and repair

nucleus

- Contains the genetic material, which codes for a particular protein
● Enclosed in a nuclear membrane

cytoplasm

Liquid substance in which chemical reactions occur.
● Contains enzymes (biological catalysts, i.e. proteins that speed up the rate of
reaction).
● Organelles are found in it

cell membrane

● Contain receptor molecules to identify and selectively control what enters and
leaves the cell

mitochondria

● Where aerobic respiration reactions occur, providing energy for the cell

ribosomes

● Where protein synthesis occurs.
● Found on a structure called the rough endoplasmic reticulum.

plant cell main features

Multicellular organisms
● Cells contain chloroplasts which is the site of photosynthesis: chlorophyll pigments within the
chloroplast structure absorb light from the Sun
● Cellulose cell walls which provide strength to the cell
● Contain a permanent vacuole, which stores cell sap and improves the cell’s rigidity
● Store carbohydrates as starch or sucrose

animal cell main features

Multicellular organisms
● Cells contain chloroplasts which is the site of photosynthesis: chlorophyll pigments within the
chloroplast structure absorb light from the Sun
● Cellulose cell walls which provide strength to the cell
● Contain a permanent vacuole, which stores cell sap and improves the cell’s rigidity
● Store carbohydrates as starch or sucrose

fungi main features

Body is usually organised into a mycelium of thread-like structures called hyphae which have
many nuclei but some are single-celled
● E.g. Mucor has typical hyphal structure, yeast is single-celled
● Cell walls are made of chitin
● Feed by extracellular secretion of digestive enzymes which break it down into smaller pieces, which can then be absorbed (saprotrophic nutrition)
● May store carbohydrates as glycogen
● Produce spores that can spread in the wind or between people (when parasitic)
● Can treat with fungicides

saprotrophic nutrition

extracellular secretion of digestive enzymes which break it down into smaller pieces, which can then be absorbed

protoctists main features

● Single-celled organisms
● Some have features like animals cells, such as Amoeba, that live in pond water
● Others are more like plants and have chloroplasts, such a Chlorella

bacteria main features

Single-celled and very small
● Have a cell wall, cell membrane, cytoplasm and plasmids
● Lack a nucleus but have circular chromosomes of DNA
● Some can carry out photosynthesis but they mainly eat off of other organisms, either dead or alive
● Can reproduce many times through binary fission
● Produce toxins that can damage cells

viruses main features

Viruses are small particles (much smaller than bacteria) - not living organisms
●Parasitic
○ Can only reproduce within living cells
○ Can infect every type of living organisms
○ Hijacks the cell mechanisms to create millions of copies of itself and then spreads
within the host by cell bursting
● They come in a wide variety of shapes and sizes
● Do not have a cellular structure but have one type of nucleic acid (either DNA or RNA) and a
protein coat