2.2 - Communities And Ecosystems

Question 1

Define a community

Answer 1

A community is a group of populations living and interacting with each other in a common habitat.

Question 2

Define an ecosystem

Answer 2

An ecosystem is a community and the physical environment it interacts with.

Question 3

How can respiration and photosynthesis be described

Answer 3

Respiration and photosynthesis can be described as processes with inputs, outputs and transformations of energy and matter.

Question 4

Define respiration

Answer 4

Respiration is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy. Aerobic respiration can simply be described as
glucose + oxygen = carbon dioxide + water

Question 5

What happens to energy during respiration

Answer 5

During respiration large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling the organisms to maintain relatively low entropy/high organization.

Question 6

What do primary producers do in the process of photosynthesis

Answer 6

Primary producers in the majority of ecosystems convert light energy into chemical energy in the process of photosynthesis.

Question 7

State equation for photosynthesis

Answer 7

carbon dioxide + water - glucose + oxygen

Question 8

What does photosynthesis produce

Answer 8

Photosynthesis produces the raw material for producing biomass.

Question 9

What does a trophic level show

Answer 9

The trophic level is the position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains.

Question 10

Define producer

Answer 10

Producers (autotrophs) are typically plants or algae and produce their own food using photosynthesis and form the first trophic level in a food chain. Exceptions include chemosynthetic organisms which produce food without sunlight.

Question 11

What does a feeding relationship involve

Answer 11

Feeding relationships involve producers, consumers and decomposers. These can be modelled using food chains, food webs and using ecological pyramids.

Question 12

Define ecological pyramid

Answer 12

Ecological pyramids include pyramids of numbers, biomass and productivity and are quantitative models and are usually measured for a given area and time.

Question 13

What males a pyramid narrower towards the apex

Answer 13

In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore the pyramids become narrower towards the apex.

Question 14

Define bio accumulation

Answer 14

Bioaccumulation is the build-up of persistent/ non-biodegradable pollutants within an organism or trophic level because they cannot be broken down.

Question 15

Define bio magnification

Answer 15

Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants along a food chain.

Question 16

How do toxins affect biomass and energy along a food chain

Answer 16

Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy.

Question 17

Define pyramids of Numbers

Answer 17

Pyramids of numbers can sometimes display different patterns, for example, when individuals at lower trophic levels are relatively large (inverted pyramids.

Question 18

Define pyramid of biomass

Answer 18

A pyramid of biomass represents the standing stock/storage of each trophic level measured in units such as grams of biomass per square metre (g m 2) or Joules per square metre (J m 2) (units of biomass or energy). Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a given time, but there may be marked seasonal variations.

Question 19

Define pyramid of productivity

Answer 19

Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that stock/storage is being generated. Pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain.

Question 20

What living processes are respiration used for

Answer 20

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition and some people remember these by their first letters which spell MRS GREN.

Question 21

Does respiration use oxygen

Answer 21

Respiration can use oxygen (aerobic) or not (anaerobic).

Question 22

What does aerobic respiration release

Answer 22

In aerobic respiration, energy is released and used and the waste products are carbon dioxide and water.

Question 23

State the equation for aerobic respiration

Answer 23

• Glucose + oxygen > Energy + water + carbon dioxide
• C,H,206 + 6 0, -> Energy + 12 H,0 + 6 CO,

Question 24

How does respiration increase the entropy of a system

Answer 24

Much of the energy produced in respiration is heat energy and is released (dissipated) into the environment. This increases the entropy (see 1.3) of the system while the organism maintains a relatively high level of organization (low entropy).

Question 25

Explain a broken down version of photosynthesis

Answer 25

The leaves of plants contain chloroplasts with the green pigment chlorophyll. In the chloroplasts the energy of sunlight is used to split water and combine it with carbon dioxide to make food in the form of the glucose. Glucose is then used as the starting point for the plant to make every other molecule that it needs.

Question 26

What happens in complex plant cells during photosynthesis

Answer 26

• add nitrogen and sulphur to make amino acids and then proteins,
• rearrange carbon, hydrogen and oxygen and add phosphorus to make fatty acids and lipoproteins which make up cell membranes.

Question 27

State the equations for photosynthesis

Answer 27

carbon dioxide + water light energy/chrorphyll, glucose + oxvgen

Symbol = reverse of respiration

Question 28

When do plants respire and how does water reach their roots

Answer 28

Green plants respire in the dark and photosynthesize and respire in the light. Water reaches the leaves from the roots by transpiration.

Question 29

When does a plant reach combustion point

Answer 29

When all carbon dioxide that plants produce in respiration is used up in photosynthesis, the rates of the two processes are equal and there is no net release of either oxygen or carbon dioxide. This usually occurs at dawn and dusk when light intensity is not too high. This point is called the compensation point of a plant and it is neither adding biomass nor using it up to stay alive at this point. It is just maintaining itself.

Question 30

Where does all energy come from

Answer 30

All energy on Earth comes from the Sun so solar energy (solar radiation) is the start of every food chain.

Question 31

Define food chain

Answer 31

A food chain is the flow of energy from one organism to the next.
A food chain shows the feeding relationships between species in an ecosystem. Arrows connect the species, usually pointing towards the species that consumes the other: so in the direction of transfer of biomass (and energy).

Question 32

What are the 2 ways to classify a producer

Answer 32

a. Autotrophs (green plants) which make their own food from carbon dioxide and water using energy from sunlight.
b. Chemosynthetic organisms which make their own food from other simple compounds eg ammonia, hydrogen sulphide or methane, do not require sunlight and are often bacteria found in deep oceans.

Question 33

Classify a consumer

Answer 33

Consumers (also called heterotrophs) which feed on autotrophs or other heterotrophs to obtain energy (herbivores, carnivores, omnivores, detritivores and decomposers).

Question 34

State the primary producers
- trophic level
- source of energy
- function

Answer 34

• 1st
• autotrophs: make their own food from solar energy, co2 and h2o
• provide the energy requirements of all the other tropic levels. Habitat for other organisms. Supply nutrients to the soil. Bind the soil/stop soil erosion

Question 35

State the primary consumer (herbivores)
- trophic level
- source of energy
- function

Answer 35

• 2nd
• heterotrophs : consume primary producers
• there consumers keep each other in check through negative feedback loops. They also disperse seeds

Question 36

State the secondary consumers (carnivores and omnivores)
- trophic level
- source of energy
- function

Answer 36

• 3rd
• heterotrophs: consume herbivores snd toher carnivores, sometimes PP
• pollinate flowers. Remove old diseased animals from the population

Question 37

State the tertiary consumers (carnivores and omnivores)
- trophic level
- source of energy
- function

Answer 37

• 4th
• heterotrophs: consume herbivores and other carnivores sometime PP
• pollinate flowers. Remove old and diseased animals from the population

Question 38

State the decomposers (bacteria and fungi)
- source of energy
- function

Answer 38

• Obtain their energy from dead organisms by secreting enzymes that break down the organic matter
• • Break down dead organisms
  • Release the nutrients back into the cycle
  • Control the spread of disease

Question 39

State the detritivores ( snails, slugs, maggots)
- source of energy
- function

Answer 39

• Derive their energy from detritus or decomposing organic material - dead organisms or feces or parts of an organism, eg shed skin from a snake, a crab carapace
• • Break down dead organisms
  • Release the nutrients back into the cycle
  • Control the spread of disease

Question 40

What are 2 negatives to food chains

Answer 40

• Food chains only illustrate a direct feeding relationship between one organism and another in a single hierarchy. The reality is very different.
  The diet of almost all consumers is not limited to a single food species.
  So a single species can appear in more than one food chain.
• A further limitation of representing feeding relationships by food chains is when a species feeds at more than one trophic level. Voles are omnivores and as well as eating insects, they also eat plants.
  Humans eat plants and animals and the animals may be herbivores and carnivores. We would then have to list all the food chains again that contained voles or humans but move them to the second trophic level rather than the third in a shorter food chain.

Question 41

Define ecological pyramid

Answer 41

Ecological pyramids include puramids of numbers.
biomass and productivitu and are quantitative models
and are usuallu measured for a given area and time

Question 42

What three things do ecological pyramids allow us to do

Answer 42

• they allow easy examination if energy transfers and losses
• they gube an idea of what feeds on what and what organisms exist at the different trophic levels
• they also help to demonstrate that ecosystems that are in balance

Question 43

What does a pyramid of numbers show

Answer 43

A pyramid of numbers shows the number of organisms at each trophic level in a food chain at one time - the standing crop. The units are number per unit area.

Question 44

What does the lengths of bars in a pyramid of numbers tell us

Answer 44

The length of each bar gives a measure of the relative numbers. Most pyramids are broad at their base and have many individuals in the producer (P) level. But some may have a large single plant, a tree, as the producer so the base is one individual which supports many consumers.

Question 45

What are the advantages of pyramids if numbers

Answer 45

This is a simple, easy method of giving an overview and is good at comparing changes in population numbers with time or season.

Question 46

What are the disadvantages of pyramids of numbers

Answer 46

• All organisms are included regardless of their size, therefore a pyramid based on an oak tree would be inverted (have a small bottom and get larger as it goes up the trophic levels).
• Does not allow for juveniles or immature forms.
• Numbers can be too great to represent accurately.

Question 47

Define pyramid of biomass

Answer 47

A pvramid of biomass contains the biomass (mass of each individual x number of individuals) at each trophic level. Biomass is the quantity of (dry) organic material in an organism, a population, a particular trophic level or an ecosystem.

Question 48

What are the units of a pyramid of biomass

Answer 48

The units of a pyramid of biomass are in units of mass per unit area, often grams per square metre (g m 2) or kilograms per water volume (eg, kg km 3).

Question 49

What do the bars tells us about a pyramid of biomass

Answer 49

A pyramid of biomass is more likely to be a pyramid shape but there are some exceptions, particularly in oceanic ecosystems where the producers are phytoplankton (unicellular green algae). Phytoplankton reproduce fast but are present only in small amounts at any one time. As a pyramid represents biomass at one time only, eg in winter, the phytoplankton bar may be far less than that of the zooplankton which are the primary consumers.

Question 50

What are the advantages to a pyramid of biomass

Answer 50

Overcomes some of the problems of pyramids of numbers.

Question 51

What are the disadvantages of a pyramid of numbers

Answer 51

• Only uses samples from populations, so it is impossible to measure biomass exactly.
• Organisms must be killed to measure dry mass.
• The time of the year that biomass is measured affects the result. In the case of algae, their biomass changes by large amounts during the year therefore the shape of the pyramid would depend on the season. The giant redwood trees of California have accumulated their biomass over many years yet algae in a lake at the equivalent trophic level may only have needed a few days to accumulate the same biomass. This pyramid will not show these differences.
• Pyramids of total biomass accumulated per vear by organisms at a trophic level would usually be pyramidal in shape. But two organisms with the same mass do not have to have the same energy content. A dormouse stores a large amount of fat, around 37 kJ g ‘ of potential chemical energy yet a carnivore of equivalent mass would contain larger amounts of carbohydrates and proteins, around 17 kJ g I potential energy. Some organisms contain a high proportion of non-digestible parts such as in the exoskeletons of marine crustaceans.

Question 52

Define pyramid of productivity

Answer 52

A pyramid of productivity shows the rate of flow of energy or biomass through each trophic level. It shows the energy or biomass being generated and available as food to the next trophic level during a fixed period of time. So, unlike pyramids of numbers and biomass, which are snapshots at one time, these pyramids show the flow of energy over time. They are always pyramid-shaped in healthy ecosystems as they must follow the second law of thermodynamics (1.3). They are measured in units of energy or mass per unit area per period of time, often Joules per square metre per year (J m-? yr 1). Productivity values are rates of

Question 53

Explain the super market analogy

Answer 53

The turnover of two supermarkets cannot be compared by just looking at the goods displayed on the shelves; the rate at which goods are being stocked and sold needs to be known. Both shops may have well stocked shelves but the rate of removal of goods from a city centre shop may be considerably more than a village shop. In the same way, pyramids of biomass simply represent the stock on the shelves, whereas pyramids of productivity show the rate at which that stock is being removed by customers and restocked by shop assistants.

Question 54

What happens to the energy in the supermarket analogy

Answer 54

The bars are drawn in proportion to the total energy utilized at each trophic level. As only about 10% of the energy in one level is passed on to the next, in pyramids of productivity, each bar will be about 10% of the lower one. Sometimes the term pyramid of energy is used which can be either the standing stock (biomass) or productivity. We shall avoid it here as it is confusing.

Question 55

What are the advantages of the supermarket analogy

Answer 55

• Most accurate system, shows the actual energy transferred and allows for rate of production.
• Allows comparison of ecosystems based on relative energy flows.
• Pyramids are not inverted.
• Energy from solar radiation can be added.

Question 56

What are the disadvantages of the supermarket analogy

Answer 56

• It is very difficult and complex to collect energy data as the rate of biomass production over time is required.
• There is still the problem (as in the other pyramids) of assigning a species to a particular trophic level when they may be omnivorous.

Question 57

Define bioaccumulation

Answer 57

If a chemical in the environment (eg a pesticide or a heavy metal] breaks down slowly or does not break down at all, plants may take it up and animals may take it in as they eat or breathe. If they do not excrete or digest it, it accumulates in their bodies over time. If the chemical stays in the ecosystem for a prolonged period of time the concentration builds up. Eventually the concentration may be high enough to cause disease or death.

Question 58

Define biomagnification

Answer 58

If a herbivore eats a plant that has the chemical in its tissues, the amount of the chemical that is taken in by the herbivore is greater than that in the plant that is eaten - because the herbivore grazes many plants over time. If a carnivore eats the herbivores, it too will take in more of the chemical than each herbivore contained as it eats several herbivores over time. In this way the chemical’s concentration is magnified from trophic level to trophic level. While the concentration of the chemical may not affect organisms lower in the food chain, the top trophic levels may take in so much of the chemical that it causes disease or their death.

Question 59

What is minimata bay

Answer 59

Minamata is a small factory town in Japan, dominated by one factory, the Chisso factory.
Chisso make petrochemical-based substances from fertilizer to plastics. Waste water containing methylmercury from this process was released into Minamata Bay. Between 1932 and 1968 Chisso released an estimated 24 tonnes of mercury and methylmercury into Minamata Bay. Beginning in the 1950s, several thousand people living locally started to suffer from mercury poisoning.

Question 60

What had caused the issues at minimata bay

Answer 60

Waste water containing elemental mercury and methylmercury from this process was released into Minamata Bay. Also, some bacteria can change elemental mercury to the modified form called methylmercury.
Methylmercury is easily absorbed into the bodies of small organisms such as shrimp. When the shrimp are eaten by fish, the methylmercury enters the fish. The methylmercury does not break down easily and can stay in the fish bodies for a long
dominated by one factory, the Chisso factory.
time. As the fish eat more and more shrimp, the
Chisso make petrochemical-based substances
amount of methylmercury increases. The same
from fertilizer to plastics. Waste water containing increase in concentration happens when people methylmercury from this process was released into then eat the fish. Mercury bioaccumulated in Minamata Bay. Between 1932 and 1968 Chisso
the food chain. People of Minamata ate a lot of
released an estimated 24 tonnes of mercury and shellfish and were poisoned by mercury. It took methylmercury into Minamata Bay. Beginning in over 30 years to recognize the cause of their the 1950s, several thousand people living locally illnesses and compensation is still being given by started to suffer from mercury poisoning.
the Chisso Corporation although the mercury release stopped in 1968.

Question 61

Why are the top carnivores in trouble

Answer 61

It is often the highest trophic level in a food chain (the top carnivore) that is the most susceptible to alterations in the environment. In the UK, the population of the peregrine falcon (a bird of prey) crashed in the late 1950s probably due to agricultural chemicals such as DDT accumulating and then magnifying in the food chain. This appeared to cause egg-shell thinning and reduced breeding success. These chemicals were banned and from the mid 1960s, the peregrine population began to slowly recover despite persecution and the threat from egg collectors.

Question 62

How much energy is transferred from one trophic level to another

Answer 62

As a rule of thumb, only 10% of the energy in one trophic level is transferred to the next - the trophic efficiency is 10%.

Question 63

State the second law or thermodynamics

Answer 63

This is a result of the second law of thermodynamics
(1.3) which states that energy is degraded to lower quality and finally to heat. More is lost because herbivores destroy more plant material than they actually eat - by trampling on it, or they reject it because it is too tough, old or spiky. Some material is not eaten at all and some dies and decomposes before it can be eaten. The 90% loss of energy in going from one trophic level to the next means there is very little energy available after about four trophic levels in terrestrial ecosystems and five in aquatic ecosystems.