GCSE OCR Gateway Biology: Paper Two

Define ecosystem

All the living organisms and physical conditions in an area

Define community

All the different species that live in an area

Define habitat

The area in which an organism lives

Define population

The total number of organisms of each species

What are producers?

Organisms that make their own food by photosynthesis

What are consumers?

Organisms that cannot make their own food and have to eat other organisms to gain energy

What are decomposers?

A special group of consumers that gain energy by feeding on dead or decaying material

Define biomass

The mass of living material present

State the ultimate source of energy for all living organisms

The sun

What is each step in a food chain called?

Tropic level

What is the disadvantage of a food chain?

Only shows organisms eating one food source

What is the advantage of a food web?

Shows animals eating more than one type of organism

Define biotic factor

A living factor

Define abiotic factor

A non-living factor

Give three examples of biotic factors

Animals, plants, fungi

Give three examples of abiotic factors

Water availability, soil pH, light intensity

What do species compete for?

Food, mates, shelter, water

How does moisture level affect an ecosystem?

Many plants cannot survive in waterlogged soil as their roots cannot respire. Certain plants are adapted to high moisture levels.

Define interdependence

How different organisms depend on each other within a community

Name the main ecological relationships?

Predation, mutualism, parasitism

What is a mutualistic relationship?

Where both organisms benefit from the relationship

What is a parasitic relationship?

Where one organisms benefits while another suffers

Give an example of a parasitic relationship

Tapeworms in a digestive system

What does a pyramid of biomass show?

The biomass of each organism in a food chain

What does a pyramid of numbers show?

The population at each trophic level

What does the bar width show in a pyramid of numbers?

The number of organisms present

State a disadvantage of collecting biomass data

Dry mass required so the organism must be dead

How do you calculate biomass?

Calculate the dry mass of an organism, multiply it by the number of organisms present

State the main reason why not all energy from the sun is transferred to chemical energy in the plant

Needed for cellular respiration

How is biomass lost?

Not all of an organism is eaten, some of the biomass used in respiration, egestion, excretion

Define egestion

When parts of an organism that cannot be digested are removed from the body in faeces

Define excretion

The process in which waste products are removed from the body

How does respiration cause biomass to decrease?

Respiration produces ATP which the muscles then use for movement. Also causes thermal energy to transfer to the environment

What is the calculation for efficiency of biomass transfer?

(Biomass after/biomass before)*100

How is carbon cycled through the atmosphere?

Released during aerobic respiration and the burning of fossil fuels, produced by photosynthesis

What do organisms use nitrogen for?

To make DNA and proteins

How is nitrogen absorbed?

By nitrogen fixing bacteria in the soil and roots

What do nitrogen fixing bacteria do?

Convert nitrogen in the air into nitrates in the soil so they can be absorbed by plants

How is nitrogen released into the atmosphere?

In waste products, dead remains

What happens to nitrogen once it has been released through waste products?

Decomposing bacteria converts it to ammonia, nitrifying bacteria converts ammonia into nitrates

How is nitrogen removed from the cycle?

Denitrifying bacteria breaks down nitrates into nitrogen

What do plants use nitrates for?

To make amino acids

How can farmers keep levels of nitrates high in plants?

Use fertilisers, crop rotation

What is crop rotation?

Using crops that produce nitrogen fixing bacteria to increase nitrates in the soil

How is water released into the atmosphere?

Precipitation, percolation,

How is water returned back to the atmosphere?

Transpiration, evaporation, condensation

Define percolation

When water trickles through gaps in soils and rocks

How is carbon used for growth?

Used to produce glucose which is then used to make complex carbohydrates like starch

What is the disadvantage of carbon dioxide?

Contributes to global warming

Define detritivore

Small animals that speed up decomposition by shredding organic material into very small pieces, giving a larger surface area for decomposers to work on

What are saprophytes?

Microorganisms that live and grow off dead or decaying organic matter

Give an example of a detritivore and what material it breaks down

Earthworm breaking down leaves

How do decomposers release nutrients?

They release enzymes which breaks down substances. They can then absorb soluble nutrients into their bodies and use them for growth. They are then eaten by other organisms, resulting in the nutrients being passed on

What are the optimum conditions for decomposition?

Warm temperature, moist environment, aerobic conditions

Why does a warm temperature increase decomposition rate?

The enzymes used by microorganisms are working at their optimum

Define variation

The differences between individuals

What causes variation?

Changes in the environment, DNA, mutatjons

Define continuous variation

Characteristics that change over a range of values

Give an example of continuous variation

Height

Define discontinuous variation

Characteristics that can be one of a limited number of options

Give two examples of discontinuous variation

Eye colour and blood group

What type of variation is only affected by inherited factors?

Discontinuous

What kind of graph could you use to represent continuous variation?

Histogram

What kind of graph could you use to represent discontinuous variation?

Bar chart

What is asexual reproduction?

The production of genetically identical offspring from a single parent

What is sexual reproduction?

Reproduction involving 2 parent organisms combining genetic material to create diverse offspring

What are gametes?

Sex cells

What is a zygote?

A fertilised egg

How many chromosones do gametes have?

23

How many cells do normal body cells have?

46

What are the advantages of asexual reproduction?

Efficient, good gene pool maintained

What are the disadvantages of asexual reproduction?

No variation so a disease could wipe out the entire species

What is the advantage of sexual reproduction?

Variation in offspring leads to adaptations in species

What are the disadvantages of sexual reproduction?

Slower than asexual so fewer offspring produced, requires two parents

Define meiosis

Type of cell division that produces four haploid cells to produce gametes

Describe the process of meiosis

Chromosomes are copied, they line up on the equator in pairs, spindle fibres pull one of each pair to opposite poles of the cell, new nucleus forms around the set of chromosomes, cell membrane pinches in, cell divides. Process repeats again to produce 4 haploid cells

State two similarities between mitosis and meiosis

Both are types of cell division, both have diploid parent cells

State two differences between meiosis and mitosis

Mitosis is used for growth and repair whereas meiosis is used to produce gametes, mitosis has one cell division whereas meiosis has two, mitosis has genetically identical daughter cells whereas meiosis does not, mitosis produces two diploid cells whereas meiosis produces four haploid cells

What is a diploid cell?

Normal body cells with two sets of chromosomes

Define genome

The whole of the genetic information of an organism

In what circumstance would two people have the same genome?

If they're identical twins

Define chromosome

A strand of DNA containing genes

Define gene

A section of DNA that codes for a specific protein

Define allele

Different form of the same gene

Define phenotype

Physical appearance of an organism

Define genotype

The alleles that an organism possesses

Define homozygous

When the two alleles are identical

Define heterozygous

When the two alleles are different

What happens if the dominant allele is present?

The characteristic is expressed

What has to happen in order for a recessive allele's characteristic to show up?

Must be present on both chromosomes

What sex chromosomes do males possess?

XY

What sex chromosomes do females possess?

XX

What is the difference between allele and variant?

They are the same thing

Define haploid cell

A cell containing only one set of chromosomes

Define mutation

A change in the base sequence of DNA

What increases risk of mutations?

Ionising radiation, ethanol, benzene

When do mutations occur?

Randomly when the DNA doesn't replicate properly

How often do mutations affect a phenotype?

Rarely

Name some harmful mutations

Cystic fibrosis, cancer

Name a beneficial mutation

Antibiotic resistance