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How would you calculate a percentage change / percentage increase / percentage decrease?

change
\--------- x 100
original

How can a scientist make their results more reliable?

Repeat the experiment.
If the experiment is on people, they could include more people in the trial (increase their sample size).

How do you set up a valid experiment?

You should ensure that you only change the independent variable. All other variables must be controlled.

What is the independent variable?

The factor that you are deliberately changing from trial to trial.

What is the dependent variable?

The thing that you are measuring in the experiment (the results).

When setting up a table of results, what goes in the left hand side column and what goes in the right hand side column?

The independent variable goes in the left hand side column. The dependent variable goes in the right hand column.

How can you get full marks for the label of a graph axis?

Copy the heading of the table over EXACTLY and remember to include units if they are needed.

How can you get full marks for making a scale on a graph?

Ensure that;

• the numbers go beyond the highest data point

• the scale allows you to plot a curve that takes up more than 50% of the y axis

• the scale means that you don't need to break a box into thirds etc when you are plotting (you can only split a box in half accurately).

What is the overall (summary) word equation for photosynthesis?

carbon dioxide + water -\> sugar + oxygen

What is the name of the pigment that traps light energy and in what part of a plant cell is it found?

chlorophyll, in the chloroplast

Describe what happens during the stage 1 of photosynthesis (the light reactions).

Light energy is converted into chemical energy (ATP):

1. Water is split to produce hydrogen and oxygen.

2. The energy released is used to generate ATP

3. Oxygen diffuses from the cell.

Which two products of the light reactions are required for stage 2 of photosynthesis (carbon fixation)?

ATP and hydrogen

What is carbon fixation (stage 2 of photosynthesis)?

A series of enzyme-controlled reactions, which use hydrogen and ATP (produced by the light reactions) with carbon dioxide to produce sugar.

What happens to the chemical energy in the sugar that is produced during photosynthesis?

1. Some of it is used for respiration

2. Some of it is turned into a structural carbohydrate (cellulose)

3. Some of it is turned into a storage carbohydrate (starch)

Name an example of a limiting factor for photosynthesis and plant growth.

1. carbon dioxide concentration

2. light intensity

3. temperature

How can a farmer increase the photosynthetic rate and therefore growth of her crops?

She could increase the carbon dioxide concentration in a greenhouse, or increase light intensity by adding artificial lighting, or increase temperature by adding heaters.

Why has there been a demand for higher food yield in recent years?

There has been an increase in the human population.

Why do farmers use fertilisers?

Fertilisers provide chemicals such as nitrates. By increasing nitrate content of the soil they can increase crop yield.

Why do farmers use pesticides?

Plants and animals that reduce plant yield can be killed by pesticides.

What happens to the nitrates that are dissolved in soil water?

1 - absorbed by plants. 2 - plants use nitrates to make amino acids 3 - plants use amino acids to make plant proteins

How do animals get amino acids for making animal proteins?

They eat plants or other animals to get amino acids.

What is the cause of algal blooms?

Fertilisers leach into fresh water, adding extra unwanted nitrates. This will increase algal populations which can cause algal blooms.

Why do algal blooms kill aquatic plants?

They reduce light levels.

Why do algal blooms cause an increase in the number of bacteria in fresh water?

Algal blooms kill aquatic plants. The dead aquatic plants and the algae become food for decomposing bacteria, which allows them to increase in number.

Following an algal bloom there is an increased number of decomposing bacteria in the water. Name a negative consequence of having more bacteria in the water.

The bacteria use up oxygen when they respire, reducing oxygen availability for other organisms.

What are some problems associated with using pesticides (such as DDT) on crops?

• pesticides can accumulate in the bodies of organisms over time

• they are passed along the food chain

• the toxicity increases to lethal levels

What are two ways of increasing plant yield without using pesticides?

• biological control

• Create GM (genetically modified) crops that resist pests.

What is an alternative to using fertilisers?

We can use genetically modified (GM) crops that are better able to grow in low nitrate soils.

What is biological control?

The use of a predator or parasite to control a pest species.

Give an example of biological control

- Controlling aphids by releasing ladybirds (their predators)

What is a mutation?

A random change to genetic material.

What are the three types of mutation that can arise?

• neutral

• advantageous to survival

• disadvantageous to survival

Why are mutations important in evolution?

They are the only source of new alleles.

Name a factor that can increase the rate of mutation.

• radiation (e.g. X-rays and UV light)

• some chemicals (e.g. mustard gas).

What is an adaptation?

An inherited characteristic that makes an organism well suited to survival in its
environment/niche.

Describe the process of natural selection in four main points.

• species produce more offspring than the environment can sustain.

• Survival of the fittest occurs when there are selection pressures.

• The best adapted individuals in a population survive to reproduce passing on their favourable alleles

• these alleles increase in frequency within the population

What is speciation?

The formation of two different species from one.

Give an example of an isolation barrier in speciation.

• geographical

• ecological

• behavioural

Why are isolation barriers important in speciation?

They stop the populations Interbreeding.

Describe the process of speciation in four main points.

• two populations of a species become isolated by a barrier

• different mutations occur in each sub-population.

• natural selection selects for different mutations in each group due to different selection pressures.

• each population evolves until they become so genetically different they are two different species.

Energy is transferred from one level of the food chain to the next. How much of this energy is used for growth?

Very little.

The majority of energy is lost when it is transferred to one level of the food chain to another. How is it lost?

• heat

• movement

• undigested material

Some food chains make irregular pyramids of numbers, as the producer may be a large organism (e.g. oak tree). How would you represent this food chain as a true pyramid?

By creating a pyramid of energy.

Which type of organism is found at the base of a pyramid of numbers or pyramid of energy?

The producer

Which type of organism is found at the apex (tip) of a pyramid of numbers or pyramid of energy?

The top level consumer

Give an example of a biotic factor that could affect biodiversity.

• competition for resources

• disease

• food availability

• grazing

• predation

Give an example of an abiotic factor that could affect biodiversity.

• light intensity

• moisture

• pH

• temperature

What is an ecosystem?

All the organisms (the community) living in a particular habitat and the non-living components with which they interact.

What is a niche?

The role that an organism plays within a community (it relates to the resources it requires in the ecosystem, such as light and nutrients, and its interactions with other organisms in the community. It involves competition and predation and the conditions it can tolerate, such as temperature).

Name a method that could be used to sample crawling insects in a woodland community.

Pitfall trap

Name a possible source of error associated with setting up a pitfall trap.

• Traps left too long/not checked regularly

• Trap not level with soil surface

• Trap not camouflaged

• No drainage holes

How could a researcher ensure that she got reliable results when using a pitfall trap?

Set many traps (repeat the sampling procedure).

Name a method that could be used to sample plants growing in a field.

Quadrat

How could a researcher eliminate bias when using a quadrat?

Throw the quadrat randomly.

Name an abiotic factor that could be measured and describe how to measure it.

• Light / using a light meter

• Temperature / using a thermometer

• pH / using a pH meter

• soil moisture / using a moisture meter

Describe a possible source of error when using a moisture meter or pH meter.

Contamination from a previous sample. You should wipe the probe between readings.

Describe a possible source of error when using a light meter.

Casting your own shadow over the meter.

Describe a possible source of error when using a thermometer.

Not allowing enough time before taking a reading.

When does competition in an ecosystem occur?

When resources are in short supply.

What is interspecific competition?

Competition between individuals of different species, for one or a few of the resources that they require.

What is intraspecific competition?

Competition between individuals of the same species for ALL of the resources that they require.

Which type of competition is more intense, interspecific competition or intraspecific competition?

Intraspecific competition.

What is a species?

A group of organisms that can interbreed to produce fertile offspring.

What is a population?

A group of organisms of the same species, living together in the same habitat.

What is a producer?

An organism that can produce its own food by photosynthesis.

What is a consumer?

An organism that gets its energy by consuming other organisms.

What is a herbivore?

An organism that gets its energy by consuming producers.

What is a carnivore?

An organism that gets its energy by consuming other consumers.

What is an omnivore?

An organism that gets its energy by consuming both producers and consumers.

In a predator-prey relationship, which organism is the predator and which is the prey?

The predator is the organism that is trying to capture and consume the other. The prey is the organism that is trying to escape the predator.

What is an indicator species?

Species that indicate environmental quality or levels of pollution by their presence, absence or abundance.

Name the type of specialized cell found in a plant root that is responsible for absorption of water by osmosis.

Root hair cells

Name a feature of a root hair cell that allows it to absorb water efficiently.

It has a large surface area.

Name the tissue that transports water and minerals up a plant.

Xylem

Name the tissue that transports sugar around a plant.

Phloem

Name the mineral found in xylem that allows it to withstand the pressure changes as water moves through the plant.

Lignin

What is transpiration?

The loss of water through stomata of the leaves (by diffusion).

Which cells are responsible for opening and closing the stomata?

Guard cells.

Where are stomata (and therefore guard cells) usually located in a leaf?

In the lower epidermis.

What is the function of mesophyll cells in the leaf?

They photosynthesise

What tissue is responsible for transporting sugar up and down the plant?

Phloem

Which of the following tissues contain living cells?
a) xylem
b) phloem

Phloem

Name the two cell types found in the leaf that are responsible for the most of the photosynthesis that takes place in a plant.

Spongy mesophyll and palisade mesophyll.

Which leaf structures contains both xylem and phloem tissue, and provides the mesophyll cells with water for photosynthesis?

Veins.

Which substances must be absorbed into the bloodstream to be delivered to cells for respiration?

Oxygen and nutrients from food (e.g. glucose)

Which materials must be removed from cells into the bloodstream?

Waste substances like carbon dioxide.

In animals, how are substances like oxygen and carbon dioxide exchanged at the cellular level between the blood and tissues?

By capillary networks.

Surfaces involved in the absorption of materials have certain features in common. Name three.

• large surface area

• thin walls

• extensive blood supply

Why do surfaces involved in absorption have a large surface area?

To increase the efficiency of absorption.

Why do surfaces involved in absorption have thin walls?

To increase the efficiency of absorption.

Why do surfaces involved in absorption have an extensive blood supply?

To increase the efficiency of absorption.

What is the organ of gas exchange in animals?

The lungs.

Where in the lungs are gases exchanged?

At the alveoli.

What is the organ of nutrient absorption in animals?

The small intestine.

Where in the small intestine are nutrients absorbed?

At the villi (singular villus)

Where do glucose and amino acids go when absorbed through the villi walls?

Into the capillary network.

Where do fatty acids and glycerol go when absorbed through the villi walls?

Into the lacteal.

What is discrete variation?

Discrete variation is where measurements fall into distinct groups or categories.

What is continuous variation?

Continuous variation is where a characteristic can have any value over a range, from minimum to maximum.

Why do some traits show discrete variation?

As they have single gene inheritance (they are controlled by only one gene).