Characteristics of Living Organisms (Edexcel IGCSE Science (Double Award): Biology): Flashcards
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What does the acronym MRS C GREN stand for?
The eight life processes shared by all living organisms:
Movement
Respiration
Sensitivity
Control
Growth
Reproduction
Excretion
Nutrition
True or False?
Reproduction is the only life process that viruses appear to carry out.
True.
Viruses are not considered living because they do not carry out all eight life processes for themselves. Even to reproduce, they must take over a host cell's metabolic pathways.
How does nutrition in plants differ from nutrition in animals?
Plants make their own food by photosynthesis, using sunlight, carbon dioxide and water.
Animals consume other living organisms and break the large molecules down by digestion into simpler molecules they can absorb.
Define respiration.
A chemical process carried out in all living organisms in which energy is released from glucose, either in the presence of oxygen (aerobic) or in its absence (anaerobic).
Respiration releases energy from glucose and transfers it in the form of ＿＿＿＿＿＿＿＿.
Respiration releases energy from glucose and transfers it in the form of ATP.
Define excretion.
The removal of toxic materials and the waste products of metabolic reactions from an organism.
How does excretion differ from egestion?
Excretion removes waste that has come from chemical reactions inside cells, such as carbon dioxide, water and urea.
Egestion removes faeces — the remains of food that was never absorbed during digestion.
Urea is a nitrogen-containing waste product formed in animals from the breakdown of ＿＿＿＿＿＿＿＿.
Urea is a nitrogen-containing waste product formed in animals from the breakdown of proteins.
Define sensitivity.
The ability of an organism to detect and respond to stimuli in its surroundings.
What is the difference between geotropism and phototropism?
Geotropism is a plant's growth response to gravity, which makes roots grow down into the soil.
Phototropism is a plant's growth response to light, which makes shoots grow towards sunlight.
Define locomotion.
The movement of an organism from one place to another.
True or False?
Plants show no movement at all.
False.
Plants cannot move from place to place, but they can change their orientation — for example, sunflowers track the sun through the day.
Define homeostasis.
The control of an organism's internal conditions so that they are kept within required limits.
Name two ways the human body responds to a rise in body temperature.
Sweating
Vasodilation
Both return the body to its optimum temperature of 37 °C.
Which waste products do plants excrete?
Oxygen, a waste product of photosynthesis
Carbon dioxide, a waste product of respiration
Both are lost through the stomata of the leaf.
How does sexual reproduction differ from asexual reproduction?
In sexual reproduction, male and female gametes fuse, so the offspring's DNA comes from both parents.
In asexual reproduction there is only one parent, so the offspring is a clone with DNA identical to the parent's.
Define growth.
A permanent increase in size.
Animals grow between the zygote and adult stage, with changes in shape and proportion. Plants keep growing throughout their whole life, forming new shoots, leaves and branches year after year.
Define eukaryotic organism.
An organism whose cells contain a nucleus surrounded by a distinct membrane.
Eukaryotes may be multicellular or single-celled.
Name the four groups of eukaryotic organisms.
Animals
Plants
Fungi
Protoctists
All eukaryotic cells contain a ＿＿＿＿＿＿＿＿ surrounded by a distinct membrane.
All eukaryotic cells contain a nucleus surrounded by a distinct membrane.
Give two ways a prokaryotic cell differs from a eukaryotic cell.
Prokaryotes have no nucleus — their genetic material sits in the cytoplasm as a single circular chromosome of DNA
Prokaryotes are always single-celled, and their cells are substantially smaller
State three features of animal cells.
Multicellular, with a nucleus in a distinct membrane
No cellulose cell walls and no chloroplasts, so they cannot photosynthesise
Carbohydrate is often stored as glycogen
Which two features of animals are linked to finding food and escaping danger?
Nervous coordination
The ability to move from place to place
What are plant cell walls made of?
Cellulose.
As which carbohydrates do plants store their food?
Starch or sucrose.
This contrasts with animals and fungi, which store carbohydrate as glycogen.
True or False?
All fungi are multicellular.
False.
Most fungi are multicellular, such as Mucor, but some are single-celled — for example, yeast.
Define hyphae.
The thread-like structures that make up the body of a multicellular fungus. Each one contains many nuclei.
Define mycelium.
The network of hyphae that forms the body of a multicellular fungus.
Define saprotrophic nutrition.
Feeding by secreting digestive enzymes outside the body onto food, usually decaying organic matter, and then absorbing the digested products.
What are fungal cell walls made of?
Chitin.
Why are protoctists described as a very diverse group?
Because they have features unlike the other three eukaryotic groups, and unlike each other:
Some are animal-like, such as Amoeba and Plasmodium
Some are plant-like, with cell walls and chloroplasts, such as the green alga Chlorella
Are protoctists single-celled or multicellular?
Microscopic and single-celled.
The protoctist ＿＿＿＿＿＿＿＿ is a pathogen that causes malaria in humans.
The protoctist Plasmodium is a pathogen that causes malaria in humans.
True or False?
Plants, fungi and protoctists all lack nervous coordination.
True.
Of the four eukaryotic groups, only animals usually have nervous coordination.
Define prokaryotic organism.
A single-celled organism whose cell has no nucleus, with its nuclear material found in the cytoplasm.
Bacteria are prokaryotic organisms.
State three features shown by all prokaryotic organisms.
They are single-celled
They have no nucleus
Their nuclear material is found in the cytoplasm
Which four structures are found in a bacterial cell?
Cell wall
Cell membrane
Cytoplasm
Plasmids
Bacteria lack a nucleus but contain a circular chromosome of ＿＿＿＿＿＿＿＿.
Bacteria lack a nucleus but contain a circular chromosome of DNA.
True or False?
Bacterial cells contain mitochondria.
False.
Bacteria lack mitochondria and have no other membrane-bound organelles.
How are bacteria described in terms of size and cell number?
They are microscopic, single-celled organisms.
Name the rod-shaped bacterium used to make yoghurt from milk.
Lactobacillus bulgaricus.
Name the spherical bacterium that causes pneumonia.
Pneumococcus.
How do most bacteria feed?
On other living or dead organisms.
Only some bacteria can photosynthesise and make their own food.
True or False?
No bacteria are able to photosynthesise.
False.
Some bacteria can photosynthesise, although most feed off other living or dead organisms.
Define plasmid.
A small circular loop of DNA in a bacterial cell, separate from its main circular chromosome.
Where is the genetic material found in prokaryotes and in eukaryotes?
Prokaryotes — in the cytoplasm
Eukaryotes — in a nucleus
Do all prokaryotic cells have a cell wall?
Yes — all prokaryotes have a cell wall.
Only some eukaryotes do, such as plants and fungi.
＿＿＿＿＿＿＿＿ are prokaryotic organisms, so their cells have no nucleus.
Bacteria are prokaryotic organisms, so their cells have no nucleus.
Define pathogen.
An organism that causes disease in another organism.
Name the four groups of organisms that include pathogens.
Bacteria
Fungi
Protoctists
Viruses
Describe the shapes and sizes of viruses.
They have a wide variety of shapes and sizes, and are always smaller than bacteria.
Name the disease each of the three named viruses causes.
Tobacco mosaic virus — discolouring of the leaves of tobacco plants
Influenza virus — flu
HIV — AIDS
True or False?
All pathogens are bacteria.
False.
Pathogens may also be fungi, protoctists or viruses.
Which organism causes severe malaria in humans?
The protoctist Plasmodium falciparum.
Viruses are small particles that are always smaller than ＿＿＿＿＿＿＿＿.
Viruses are small particles that are always smaller than bacteria.
True or False?
Viruses are classified as living organisms.
False.
Viruses are not considered living because they do not carry out the eight life processes for themselves.
State four characteristics shared by all viruses.
They are small particles, always smaller than bacteria
They are parasitic and can reproduce only inside living cells
They infect every type of living organism
They have no cellular structure, but a protein coat around one type of nucleic acid
A virus has no cellular structure, but has a protein coat containing one type of nucleic acid, either DNA or ＿＿＿＿＿＿＿＿.
A virus has no cellular structure, but has a protein coat containing one type of nucleic acid, either DNA or RNA.
Why can a virus only reproduce inside a living cell?
Because it is parasitic and has no cellular structure of its own, so it must take over a host cell's metabolic pathways to make copies of itself.
What symptom does tobacco mosaic virus cause in plants?
A distinctive mosaic pattern of discolouration on the leaves.
The virus infects the chloroplasts and prevents them from forming.
What surrounds the nucleic acid of a virus?
A protein coat. A virus has no cellular structure at all.
Which types of living organism can viruses infect?
Every type of living organism.
True or False?
A virus can reproduce on its own, outside a living cell.
False.
Viruses are parasitic and can reproduce only inside living cells.
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