Communities and Ecosystems

Question 1

What is a community?

Answer 1

A community is a group of populations living and interacting with each other in a common habitat (the same place)

Question 2

What is an ecosystem?

Answer 2

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

Question 3

What is a tropical rainforest a community of?

Answer 3

A tropical rainforest is a community of plants and animals, bacteria and fungi

Question 4

Do ecosystems exist independently?

Answer 4

Ecosystems do not exist independently but interact to make up the biosphere

Question 5

What is respiration?

Answer 5

Respiration is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy

Aerobic respiration can be described as:

glucose + oxygen -> carbon dioxide + water

Question 6

How is entropy in an ecosystem increased during respiration?

Answer 6

During respiration, large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem whilst enabling the organisms to maintain relatively low entropy

Question 7

Primary producers in the majority of ecosystems convert light energy into chemical energy. What is this process called?

Answer 7

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

This is a transformation of energy from one state to another.

Question 8

What is photosynthesis?

Answer 8

Photosynthesis is the process by which green plants make their own food from water and carbon dioxide using energy from sunlight

Question 9

How does photosynthesis work?

Answer 9

• Leaves of plants contain chloroplasts with green pigment chlorophyll
• In chloroplasts, energy of sunlight is used to split water + combine it with CO2 to make glucose
• Glucose is then used as the starting point for the plant to make every other molecule it needs
  e. g. plants add nitrogen + sulphur to make amino acids (+ then proteins)

Question 10

What produces the raw material for producing biomass?

Answer 10

Photosynthesis produces the raw material for producing biomass

Question 11

What is the equation for photosynthesis?

Answer 11

carbon dioxide + water -> glucose + oxygen

Question 12

When do green plants respire?

Answer 12

When it is both dark and light

Question 13

When do green plants photosynthesise?

Answer 13

Only when it is light

Question 14

How does water reach the leaves of plants?

Answer 14

Water reaches the leaves from the roots by transpiration

Question 15

What is the compensation point of a plant?

Answer 15

• When all CO2 that plants produce in respiration is used up in photosynthesis, the rates of the 2 processes are equal
• There is no net release of oxygen or CO2
• This occurs at dawn / dusk when light intensity is not too high
• This point is called ‘compensation point’
• At this point, plant is neither adding biomass or using it up to stay alive
• It is just maintaining itself

Question 16

What is a trophic level?

Answer 16

A 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 17

Where does all energy on Earth come from?

Answer 17

All energy on Earth comes from the Sun so solar energy is the start of almost every food chain

Question 18

If organisms don’t get their energy from the Sun, where do they get it from?

Answer 18

Some deep ocean vents give out heat from the Earth’s mantle and some organisms get their energy from this through a process called chemosynthesis

Question 19

What is a food chain?

Answer 19

• 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 (+ energy)

Question 20

What do trophic levels usually start with?

Answer 20

A primary producer (plant)

Question 21

What do trophic levels usually end with?

Answer 21

A carnivore at the top of the chain (A top carnivore)

Question 22

What are autotrophs?

Answer 22

Green plants that make their own food from carbon dioxide and water using energy fro sunlight

Question 23

What are chemosynthetic organism?

Answer 23

Make their own food from other simple compounds e.g. ammonia, hydrogen sulphide or methane, do not require sunlight and are often bacteria found in deep oceans

Question 24

What are consumers (also called heterotrophs) ?

Answer 24

Feed on autograph or other heterotrophs to obtain energy

herbivores, carnivores, omnivores, detritivores, decomposers

Question 25

What is the function of primary producers?

Answer 25

- Provide the energy requirements of all other trophic levels - Habitat for other organisms - Supply nutrients to the soil - Bind the soil // stop soil erosion

Question 26

What is the function of consumers (heterotrophs) ?

Answer 26

- Keep each other in check through negative feedback loops - Disperse seeds - Pollinate flowers - Remove old + diseased animals from the population

Question 27

Give 2 examples of decomposers

Answer 27

Bacteria | Fungi

Question 28

Give 4 examples of detritivores

Answer 28

Snails Slugs Maggots Vultures

Question 29

What is the function of decomposers and detritivores ?

Answer 29

Provides a crucial service for ecosystem - break down dead organisms - release the nutrients back into the cycle - control the spread of disease

Question 30

What are 2 limitations of food chains?

Answer 30

- Food chains only illustrate a direct feeding relationship between one organism and another in a single hierarchy - But diet of almost all consumers not limited to single food species - Species may feed at 1+ trophic levels - eg. voles = omnivores (eat insects + plants)

Question 31

What is a food web?

Answer 31

A complex network of interrelated food chains. Closer to reality than single food chain.

Question 32

What are ecological pyramids?

Answer 32

- Ecological pyramids include pyramids of numbers, biomass + productivity - quantitive models - usually measured for a given area and time

Question 33

3 good things about ecological pyramids

Answer 33

- allow easy examination of energy transfers + losses - give an idea of what feeds on what, and what organisms exist at diff. trophic levels - help demonstrate that ecosystems are balanced systems

Question 34

What does a pyramid of numbers show?

Answer 34

A pyramid of numbers shows the number of organisms at each trophic level in a food chain at one time - the STANDING CROP.

Question 35

Are all pyramids of numbers broad at their base?

Answer 35

- Most pyramids of numbers are broad at their base + have many individuals in the Producer level - But some may have a large single plant (e.g. tree) as Producer so base is 1 individual that supports many consumers

Question 36

2 advantages of pyramids of numbers

Answer 36

- simple, easy method of giving an overview | - good at comparing changes in pop. numbers with time or season

Question 37

3 disadvantages of pyramids of numbers

Answer 37

- all organisms included regardless of their size (so pyramid based on an oak tree would be inverted) - does not allow for juveniles / immature forms - numbers can be too great to represent accurately

Question 38

What is a pyramid of biomass?

Answer 38

- A pyramid of biomass contains the biomass (mass of each individual x no. individuals) at each trophic level - Biomass is the quantity of dry organic material in an organism, a population, trophic level or ecosystem

Question 39

What are the units of a pyramid of biomass?

Answer 39

Tend to be: > grams per square metre (g m^-2) > kilograms per water volume (kg km^-3)

Question 40

A pyramid of biomass is more likely to be a pyramid shape. Are there any exceptions?

Answer 40

> In oceanic systems producers are phytoplankton > Phytoplankton reproduce fast but are present only in small amounts at any time > As pyramid represents biomass at one time only e.g. winter, the phytoplankton bar may be much smaller than zooplankton bar (primary consumers)

Question 41

Advantage of pyramid of numbers

Answer 41

Overcomes some of the problems of pyramids of numbers

Question 42

4 disadvantages of pyramids of numbers

Answer 42

Only uses samples from populations, so impossible to measure biomass exactly Organisms killed to ensure dry mass Time of year biomass is measured affects results. e.g giant redwood trees (california) have accumulated biomass over years, but algae in lake at equivalent trophic level only a few days to accumulate same biomass. Pyramid won't show these differences 2 organisms w same mass may not have same energy content. e.g. dormouse stores a lot of fat yet a carnivore of equivalent mass would contain larger amounts of carbs + proteins

Question 43

What does a pyramid of productivity show?

Answer 43

- Rate of flow of energy // biomass through each trophic level - Shows energy or biomass being generated + available as food to next trophic level during fixed period of time - Always pyramid-shaped in healthy ecosystems as must follow 2nd Law of Thermodynamics

Question 44

How are the bars drawn in pyramids of productivity?

Answer 44

- drawn in proportion to total energy utilised at each trophic level - as only 10% energy passed on to next level, each bar will be about 10% of the lower one

Question 45

4 advantages of pyramids of productivity

Answer 45

- Most accurate system, shows actual energy transferred + 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 46

2 disadvantages of pyramids of productivity

Answer 46

- very difficult + complex to collect energy data as rate of biomass production over time is required - still the problem (as in other pyramids) of assigning organisms particular trophic level when they may be omnivores

Question 47

What is bioaccumulation?

Answer 47

- If chemical (e.g. pesticide / heavy metal) doesn't break down, organisms may ingest or absorb it - If chemical stays in ecosystem for a long time, the concentration builds up - Concentration may be high enough to cause disease // death

Question 48

What is biomagnification?

Answer 48

- If a herbivore eats many plants with chemicals in their tissues, the herbivore will take in more chemical than each individual plant has - If a carnivore eats the herbivores, it too will take in more chemical than herbivore because eats several herbivores over time - So chemical's concentration is magnified from trophic level to trophic level - Lower trophic levels may not be affected - But top trophic levels may take in so much chemical it causes disease // death

Question 49

Case Study Minamata Bay, Japan // what did Chisso factory do that was so bad?

Answer 49

- Chisso make petrochemical-based substances from fertiliser to plastics - Waste water containing methylmercury from this process was released into Minamata Bay - Between 1932-1968, released 24 tonnes methylmercury + mercury into Minamata Bay

Question 50

Case Study Minamata Bay, Japan // what did methylmercury do to shellfish?

Answer 50

- Methylmercury is easily absorbed into bodies of small organisms e.g. shrimp - When shrimp are eaten by fish, methylmercury enters fish - Methylmercury doesn't break down easily + can stay in fish for long time - As fish eat more + more shrimp, concentrations of methylmercury increase - Mercury bioaccumulated in food chain

Question 51

Case Study Minamata Bay, Japan // what happened to people living locally

Answer 51

- beginning in 1950s, thousands of people living locally suffered from mercury poisoning having eaten lots of shellfish - took 30+ years to recognise cause of their illnesses - compensation is still being given by Chisso Corporation although mercury release stopped in 1968

Question 52

Why are top carnivores always vulnerable to the effects of changes further down the chain?

Answer 52

- Top carnivores often have limited diet so a change in their food prey has knock-on effect - Their pop. numbers are low due to fall in efficiency along food chain, so their they ability to withstand negative influence is more limited