B4 - it's a green world

Question 0

What is a community and population?

Answer 0

All the animals and plants living in the garden make up the community. The number of a particular plant or animal present in the community is called its population.

Question 1

What is an ecosystem and habitat?

Answer 1

An ecosystem such a garden is made up of all the plants and animals living there and their surroundings. Where a plant or animal lives is its habitat.

Question 2

How can the distribution of organisms be mapped?

Answer 2

The distribution of organisms can be mapped using a transect line. A long length of string is laid across an area such as a path or seashore. At regular intervals the organisms in a square frame called a quadrat can be counted (for animals) or assessed for percentage cover (for plants). The data can be displayed as a kite diagram.

Question 3

What are artificial ecosystems?

Answer 3

In artificial ecosystems, humans deliberately keep and protect any one species (such as salmon in a fish farm) and remove any other organisms that would compete with it and low the yield. This does not happen in a natural ecosystem

Question 4

What is zonation and how can it be shown?

Answer 4

A transect line can show zonation in the distribution of organisms. Changes in abiotic (not biological) factors such as exposure on a sea shore or trampling near a footpath, cause zonation.

Question 5

How can you estimate a population size of an organism in an area?

Answer 5

The capture-recapture method:

Capture the organism and mark it and then release it. Later, recapture the organism.

Population size = number marked in 1st sample x number in 2nd sample/number in second sample previously marked

Question 6

What does using the capture-recapture method assume?

Answer 6

• there are no deaths or reproduction and no movement of animals into and out of the area
• identical sampling methods are used for both samples
• the markings do not affect the survival of the woodlice

Question 7

What is the balanced symbol equation for photosynthesis?

Answer 7

6CO(two) + 6H(two)O –> C(six)H(twelve)O(six) + 6O(two)

Question 8

What can the simple sugars (such as glucose) from respiration be used for?

Answer 8

Used in respiration, releasing energy.

Converted into cellulose to make cell walls.

Converted into proteins for growth and repair.

Converted into starch, fats and oils for storage

Question 9

Why is starch used for storage in plants?

Answer 9

Starch is used for storage since it is insoluble and does not move from storage areas. Unlike glucose, it does not affect the water concentration of cells and cause osmosis.

Question 10

Explain the two stages of photosynthesis.

Answer 10

• water is split up by light energy releasing oxygen gas and hydrogen ions
• carbon dioxide gas combines with the hydrogen ions producing glucose and water

Question 11

Talk me through the historical understanding of photosynthesis.

Answer 11

• Greek scientists believed that plants took minerals out of the soil to grow and gain mass
• van helmont concluded from his experiment on growing a willow tree that plant growth could not be due only to the uptake of soil minerals -it must depend on something else
• priestly’s experiment showed that plants produce oxygen

Question 12

What does the modern experiment using a green alga called chlorella and an isotope of oxygen, 18O, tell us about photosynthesis?

Answer 12

Modern experiments using a green alga called chlorella and an isotope of oxygen, 18O, as part of a water molecule, have shown that the light energy is used to split water, not carbon dioxide. The water is split up into oxygen gas and hydrogen ions. Isotopes are different forms of the same element.

Question 13

How can the rate of photosynthesis be increased?

Answer 13

When the plant has:

• more carbon dioxide
• more light
• a higher temperature which increases enzyme action

Question 14

What are the limiting factors of photosynthesis?

Answer 14

Light, temperature and carbon dioxide.

Question 15

What does a plant do throughout the day? Explain in detail.

Answer 15

Plants respire at all times by taking in oxygen and releasing carbon dioxide.

During the day, when it is light, they also carry out photosynthesis, taking in carbon dioxide and releasing oxygen: the same gas exchange as respiration but in reverse. The rate of gas exchange in photosynthesis is more than that of respiration in terms of quantities, so respiration can only be noticed at night (in darkness).

Question 16

How are cells in a leaf adapted for efficient photosynthesis?

Answer 16

• the outer epidermis lacks chloroplasts and so is transparent; there are no barriers to the entry of light
• the upper palisade lager contains most of the leaf’s chloroplasts, as they will receive most of the light
• the spongy mesophyll cells are loosely spaced so that diffusion of gases between cells and the outside atmosphere can take place
• the arrangement of mesophyll cells creates a large surface area/volume ratio so that large amounts of gases can enter and exit cells

Question 17

How are leaves adapted so that photosynthesis is efficient?

Answer 17

• they are usually broad so that they have a large surface area to get as much light as possible
• they are usually thin so that gases can diffuse through easily and light can get to all cells
• the contain chlorophyll and other pigments so that they can use light from a broad range of the light spectrum
• they have a network of vascular bundles (veins) for support and transport of chemicals such as water and glucose
• they have specialised guard cells which control the opening and closing of stomata therefore regulating the flow of carbon dioxide and oxygen as well as water loss
• they have stomata for entry and exit of gases. The spongy mesophyll cells are also covered with a film of water in which the gases can dissolve. This water can therefore readily escape through the stomata.

Question 18

What does a leaf achieve by having many pigments?

Answer 18

By having many pigments (chlorophyll a and b, carotene and xanthophylls) the plant cells can maximise the use of the Sun’s energy. Each pigment absorbs light of different wavelengths.

Question 19

What is diffusion?

Answer 19

Diffusion is the net movement of particles in a gas or liquid from an area of high concentration to an area of low concentration, resulting from the random movement of the particles.

Question 20

How are leaves adapted to increase the rate of diffusion of carbon dioxide?

Answer 20

• (usually) a large SA
• specialised openings called stomata, which are spaced out
• gaps between the spongy mesophyll cells

Question 21

How can the rate of diffusion be increased?

Answer 21

By having:

• a shorter distance for the molecules to travel
• a steeper concentration gradient (a greater difference in concentration between the two areas)
• a greater surface area for the molecules to diffuse from, or into

Question 22

What is osmosis?

Answer 22

Osmosis is the movement of water across a partially-permeable membrane from an area of high water concentration (a dilute solution) to an area of low water concentration (a concentrated solution).

Question 23

How does turgor pressure support the cell? (Hint: what causes plants to wilt?)

Answer 23

The entry of water into plant cells increases the pressure pushing on the cell wall, which is rigid and not elastic. This turgor pressure supports the cell wall, stopping it, and the whole plant collapsing. When too much water leaves a cell, it loses this pressure and the plant wilts.

Question 24

What happens to a plant cell with little/too much water?

Answer 24

A plant cell full of water is turgid. When the cell loses water the cell contents shrink and become plasmolysed and the cell is flaccid.

Question 25

What happens to an animal cell with little/too much water?

Answer 25

Animal cells also react to intake and loss of water due to osmosis.

Since animal cells lack a supporting cell wall, when too much water enters, they will swell up and burst (lysis). When too much water leaves an animals cell, it shows crenation by shrinking into a scalloped shape.

Question 26

What is the function of xylem cells?

Answer 26

Xylem cells carry water and minerals from the roots to the leaves and are therefore involved in transpiration.

The xylem cells are called vessels. They are dead cells, and the lack of living cytoplasm leaves a hollow lumen. Their cellulose walls have extra thickening of lignin, giving them great strength and support.

Question 27

How are phloem cells arranged?

Answer 27

Phloem cells are living and are arranged in columns.

Question 28

What do phloem cells do?

Answer 28

Phloem cells carry food substances such as sugars up and down stems to growing and storage tissues. This transport of food substances is called translocation.

Question 29

What is transpiration?

Answer 29

Transpiration is the evaporation and diffusion of water from inside leaves. This loss of water from leaves helps to create a continuous flow of water from the roots to the leaves in xylem cells.

Question 30

What do root hairs do?

Answer 30

Root hairs are projections from root hair cells. They produce a large surface area for water uptake by osmosis.

Question 31

What does transpiration ensure?

Answer 31

Transpiration ensures that plants have water for cooling by evaporation, photosynthesis and support from cells’ turgor pressure, and transport of minerals.

Question 32

How is the rate of transpiration increased?

Answer 32

The rate of transpiration is increased by:

• an increase in light intensity, which results in stomata being open
• an increase in temperature, causing an increase in the evaporation of water
• an increase in air movement, blowing away air containing a lot of evaporated water
• a decrease in humidity, allowing more water to evaporate

Question 33

How is the structure of a leaf adapted to prevent too much water loss?

Answer 33

• The structure of a leaf is adapted to prevent too much water loss, which could cause wilting.
• Water loss is reduced by having a waxy cuticle covering the outer epidermal cells
• and by most stomatal openings being situated on the shaded lower surface. It’s guard cells are able to change the size of the stomatal openings. The guard cells contain chloroplasts, so photosynthesis will produce sugars, increasing turgor pressure, causing the cells to swell. Due to differential thickness of their walls, the guard cells curve, opening the stoma.

Further reduction in water loss is brought about by having fewer stomata, smaller stomata, the position of stomata and their distribution.

Question 34

Plants need minerals, such as…

Answer 34

• nitrates, to make proteins, which plants use for cell growth
• phosphates, which are involved in respiration and growth
• potassium compounds, which are involved in respiration and photosynthesis
• magnesium compounds, which are involved in photosynthesis

Question 35

Which elements from soil minerals are used to produce useful compounds?

Answer 35

• nitrogen is used to produce amino acids, which combing to form a variety of proteins.
• phosphorus is used to make DNA, which contains the plant’s genetic code, and cell membranes
• potassium is used to help enzyme action in photosynthesis and respiration
• magnesium is used to make chlorophyll which is essential for photosynthesis

Question 36

What does the lack of nitrates in plant soil cause?

Answer 36

-lack of nitrate causes like growth and yellow leaves

Question 37

What does the lack of phosphate in plant soil cause?

Answer 37

Lack of phosphate causes poor root growth and discoloured leaves.

Question 38

What does the lack of potassium in plant soil cause?

Answer 38

Lack of potassium causes poor flower and root growth and discoloured leaves.

Question 39

What does the lack of magnesium in plant soil cause?

Answer 39

Lack of magnesium caused yellow leaves.

Question 40

What is active transport?

Answer 40

Active transport enables minerals, present in the soil only in low concentrations, to enter root hairs already containing higher amounts of minerals.

This uptake of minerals against a concentration gradient requires energy from respiration.

Question 41

How are minerals taken up from soil?

Answer 41

Minerals add taken up by root hair cells by active transport, rather than by diffusion or osmosis.

Question 42

What are detritivores?

Answer 42

Earthworms, maggots and woodlice are called detritivores because they feed on dead and decaying material (detritus)

Question 43

What do detritivores increase?

Answer 43

Detritivores increase the rate of decay by breaking up to detritus and so increasing the surface area for further microbial breakdown.

Question 44

How does the rate of decay increase with temperature?

Answer 44

Increasing the temperature to an optimum of 37• for bacteria or 25• for fungi will increase their rate of respiration.

Question 45

How does the rate of decay increase with the amount of oxygen?

Answer 45

By increasing the amount of oxygen, bacteria will use aerobic respiration to grow and reproduce faster.

Question 46

How does the rate of decay increase with the amount of water?

Answer 46

Increasing the amount of water will allow for material to be digested and absorbed more efficiently and increase growth and reproduction of bacteria and fungi.

Question 47

What is a saprophyte?

Answer 47

A saprophyte, for example a fungus, is an organism that feeds on dead and decaying material.

Question 48

What is extracellular digestion?

Answer 48

Fungi produce enzymes to digest food outside their cells and then transport the simple soluble substances. This type of digestion is called extracellular digestion.

Question 49

What different food preservation methods are there and how do they reduce the rate of decay?

Answer 49

• in canning, foods are heated to kill bacteria and then sealed in a vacuum to prevent entry of oxygen and bacteria
• cooling foods will slow down bacterial and fungal growth and reproduction
• freezing foods will kill some bacteria and fungi and slow down their growth and reproduction
• drying foods removes water so bacteria cannot feed and grow
• adding salt or sugar will kill some bacteria and fungi, as the osmotic concentration will remove water from them
• adding vinegar will produce very acidic conditions killing most bacteria and fungi

Question 50

What are the disadvantages of using pesticides?

Answer 50

• they can enter and accumulate in food chains causing a lethal dose to predator
• they can harm other organisms living nearby
• some are persistent (take a long time to break down and become harmless)

Question 51

What are the disadvantages of organic farming?

Answer 51

The crops are smaller and the produce more expensive.

Question 52

How do farmers make sure organic farming is efficient?

Answer 52

It uses animal manure and compost (instead of artificial fertilisers), crop rotation (to avoid build-up of soil pests), nitrogen-fixing crops as part of the rotation, and varying seed plant times to get a longer crop time and avoid certain times of the life cycle of insect pests.

Question 53

What is biological control?

Answer 53

Biological control uses living organisms to control pests. Examples are using ladybirds and certain wasp species to eat aphids, which damage plants.

Question 54

What are the advantages of biological control?

Answer 54

Biological control uses living organisms, once introduced they do not usually need replacing.

Question 55

What are the disadvantages of biological control?

Answer 55

Many attempts at biological control have caused other problems such as the introduced species eating other useful species and then showing a rapid increase in their population so they themselves become pests e.g the use of cane toads in Australia.

Introducing a species into a habitat to kill another species can affect the food sources of other organisms in a food web, causing unexpected results.

Question 56

How does intensive farming improve the efficiency of energy transfer in food chains?

Answer 56

Intensive farming improves the efficiency of energy transfer in food chains involving humans by reducing or removing competing organisms such as animal pests and weeds. Also by keeping animals inside sheds or barns (battery farming), the use less energy to keep warm and to move, and more energy on growth (cattle) or egg production (hens).