Organisation of an Ecosystem Flashcards

All 35 cards in this deck

What is a producer?

An organism that makes its own biomass (glucose) by photosynthesis, usually a green plant or alga.

Why does every food chain begin with a photosynthetic organism?

Only producers can use light energy to synthesise glucose, making the biomass that all other organisms feed on.

In a food chain, what name is given to an animal that eats a primary consumer?

A secondary consumer.

e.g. grass → rabbit (primary) → fox (secondary)

What are predators and prey?

Predators are consumers that kill and eat other animals; prey are the animals that are eaten.

True or false? In a stable community the numbers of predators and prey stay constant.

False. They rise and fall in cycles.

In a predator–prey cycle graph, which population peaks first?

The prey population peaks first; the predator population peaks shortly afterwards, because more food allows more predators to survive and breed.

What are the steps to estimate the population size of a species using quadrats?

e.g. daisies in a field of area $200\ \text{m}^2$ using $1\ \text{m}^2$ quadrats

1. Place quadrats at random positions (random number coordinates), e.g. 10 quadrats.
2. Count the species in each quadrat and find the mean per quadrat, e.g. mean $= 6$ per $\text{m}^2$.
3. Multiply the mean per $\text{m}^2$ by the total area: $6 \times 200 = 1200$ daisies.

Why must quadrat positions be chosen at random when estimating a population size?

To avoid bias, so the sample is representative of the whole habitat.

What is a transect in ecological sampling?

A line across a habitat along which quadrats are placed at intervals, used to show how distribution changes across the habitat.

What are the steps to use a transect to investigate the effect of a factor on distribution?

e.g. effect of distance from a pond on rushes

1. Lay a tape measure in a line from the pond outwards.
2. Place a quadrat at regular intervals along the line, e.g. every 2 m, and record the number or percentage cover.
3. Measure the factor at each point (e.g. soil moisture) and plot abundance against distance.

True or false? The median of a set of abundance data is the most common value.

False. The most common value is the mode; the median is the middle value when the data are put in order.

When plotting abundance data on a graph, how should you choose the scales for the axes?

Use a linear scale that spreads the data over at least half of the available graph paper, and label each axis with the quantity and unit.

Which processes return carbon to the atmosphere as carbon dioxide?

Respiration (of plants, animals and decomposers) and combustion of fuels.

Which process removes carbon dioxide from the atmosphere in the carbon cycle?

Photosynthesis by plants and algae, which converts carbon dioxide into glucose and other carbon compounds.

What is the role of microorganisms in cycling materials through an ecosystem?

They decompose dead organisms and waste, returning carbon dioxide to the atmosphere by respiration and mineral ions to the soil.

What are the steps of the water cycle?

e.g. starting with water in the sea

1. Energy from the Sun evaporates water from the seas and land, forming water vapour.
2. The vapour rises, cools and condenses into clouds, then falls as precipitation (rain or snow).
3. This fresh water is used by plants and animals on land before draining back into the seas.

True or false? Materials in the living world are used once and then lost.

False. All materials are recycled to provide the building blocks for future organisms.

True or false? Only animals respire, so only animals return carbon dioxide to the atmosphere.

False. Plants, algae and decomposing microorganisms respire and release carbon dioxide too.

Name two types of microorganism that cause decay.

Bacteria and fungi.

Which three conditions affect the rate of decay of biological material?

Temperature, water (moisture) and availability of oxygen.

How does increasing temperature affect the rate of decay?

Decay speeds up as microorganisms reproduce faster and their enzymes are more active, until the temperature is high enough to denature the enzymes and decay slows.

Why does a good supply of oxygen increase the rate of decay?

Decomposers need oxygen for aerobic respiration, which releases the energy for growth and reproduction.

Which gas is produced by anaerobic decay, and how is it used?

Methane; biogas generators use anaerobic decay of waste to produce methane as a fuel.

Which conditions do gardeners provide in a compost heap for rapid decay?

Warmth, moisture and oxygen (by turning the heap); the compost is used as a natural fertiliser.

What are the steps of the required practical on the effect of temperature on the rate of decay of milk?

e.g. testing 5 °C, 15 °C and 25 °C

1. Put the same volume of the same fresh milk into each container, e.g. $25\ \text{cm}^3$.
2. Keep each at a different constant temperature in a water bath, e.g. 5 °C, 15 °C, 25 °C.
3. Measure and record the pH at regular intervals (e.g. each day) until it reaches a set pH.

Give two control variables for the investigation into the effect of temperature on the decay of milk.

Volume of milk and type/freshness of the milk (also exposure to air and the time of day the pH is measured).

Give one way the pH of decaying milk can be measured.

Universal indicator paper or solution, or a pH meter (pH probe).

How can milk be kept at a constant temperature during the decay practical?

Place the container in a water bath (or an incubator) set to that temperature.

What are the steps to calculate the rate of pH change of decaying milk?

e.g. pH falls from 6.6 to 5.6 in 2 days

1. Find the change in pH: $6.6 - 5.6 = 1.0$.
2. Divide by the time taken: $1.0 \div 2$.
3. Rate $= 0.5$ pH units per day.

Name three environmental changes that affect the distribution of species in an ecosystem.

Temperature, availability of water, and the composition of atmospheric gases.

Environmental changes that affect distribution may be of which three kinds?

Seasonal, geographic, or caused by human interaction.

What is meant by the distribution of a species?

Where the species is found within an ecosystem or area.

Why might a species be found in a habitat during only part of the year?

Seasonal changes, such as temperature or food availability, cause it to migrate to or from the area.

True or false? Environmental change always reduces the distribution of a species.

False. A change can also increase a species' distribution or allow it to spread into new areas.

True or false? A change in the composition of atmospheric gases can change where a species is found.

True. Species differ in their sensitivity to gases such as carbon dioxide, oxygen and sulfur dioxide.