1. Biology Unit 4 – It’s a Green World
04/02/2019
OCR Gateway Additional Science
Biology Unit 4 – It’s a Green World
W Richards
The Weald School

2. B4a: Ecology in the local Environment
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B4a: Ecology in the local Environment

3. Taking samples of an ecosystem
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Using different “sampling techniques” we can measure changes in an ecosystem. The two main measurements are:
The physical conditions of a habitat (temperature etc)
The populations of different species in that habitat
Some common ways of measuring…
Help!
Measuring temp, pH etc
Taking animal samples
Taking samples using quadrats

4. Method 2 – Capture/recapture
Population Size
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There are two ways we can easily use to estimate population size:
Method 1 – Scaling up
If a 1m2 sample contains 10 woodlice how many woodlice are in a field measuring 200m by 300m?
200m x 300m x 10 woodlice per square metre = 600,000 woodlice
Method 2 – Capture/recapture
A sample contains 10 stoats and a week later a second sample contains 15 stoats of which 2 were in the previous sample. How many stoats are in the population?
Population Estimate = No. in 1st sample x no. in 2nd sample
Number in 2nd sample previously marked
No. of stoats = (10 x 15) / 2 = 75 stoats
What assumptions are we making with this method?

5. Ecosystems
04/02/2019
“Ecosystem” is a term used to describe all of the organisms living together as a community in a particular habitat and can often be self-supporting other than the need for an energy source.
Ecosystems are constantly changing:
Changes in population due to predation, disease etc
Physical changes (e.g. temperature change)
Changes in ecosystems
Human interference
Pollution
These changes can lead to “zonation” – a gradual change in species distribution over the habitat.
Changes in soil conditions

6. Transect lines and zonation
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Here are some population samples taken along a transect line along a shoreline:

7. Ecosystems
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An “Ecosystem” is a physical environment with a particular set of organisms living in it. They can be natural, e.g. a woodland, or artificial, e.g. a greenhouse.
A natural ecosystem with high “biodiversity”
An artifical ecosystem – biodiversity will be controlled and low

8. 04/02/2019
B4b: Photosynthesis

9. Photosynthesis
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Basically, photosynthesis is the process through which a plant makes its own food using carbon dioxide and water:
That’s a nice plant. I’m going to put it in the sun and give it lots of water and air…
CO2
H2O

10. Photosynthesis – the 4 things you need
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SUNLIGHT
Gives the plant energy
CHLOROPHYLL
The green stuff where the chemical reactions happen
WATER
Travels up from the roots
CARBON DIOXIDE
Enters the leaf through small holes on the underneath

11. Photosynthesis equations
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Carbon dioxide + _____ glucose + _____
6CO H20 C6H12O O2
Sunlight
Chlorophyll
The GLUCOSE produced by photosynthesis is used by the plant for _______ (through ____________). It is stored in the plant as ___________.
Words – respiration, starch, water, oxygen, energy

12. Photosynthesis over the ages
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Our understanding of how plants grow has changed over the ages:
I’m a Greek scientist and we believed that plants gained mass through taking things in from the soil.
I’m Jean Baptista Van Helmont and I showed that plant growth wasn’t possible through nutrient uptake alone.
I’m Joseph Priestley and I proved that oxygen is produced by plants.

13. How Photosynthesis works
04/02/2019
Basically, we now understand that the oxygen produced by photosynthesis comes from water:
1) Light is used to split water, releasing oxygen gas and hydrogen ions:
H2O H+ O2
C6H12O6
2) Carbon dioxide combines with the hydrogen ions to make glucose:
CO2

14. What is the glucose used for?
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1) Glucose (sugar) can be used to make long chains of insoluble starch…
Glucose molecules
Starch molecule
2) Glucose can be used to make cellulose for cell walls…
Glucose molecules
Cellulose
3) Glucose can be combined with nitrates to make proteins (for growth)…
Glucose molecules
Proteins
4) Glucose can be converted into lipids (fats or oils) to store in seeds…
Glucose molecules
Lipid structure

15. Limiting Photosynthesis
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What factors could limit the rate of photosynthesis?
Temperature – the best temperature is about 300C – anything above 400C will slow photosynthesis right down
CO2 – if there is more carbon dioxide photosynthesis will happen quicker
Light – if there is more light photosynthesis happens faster

16. Drawing graphs of these factors
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1. Temperature
Photosynthesis is controlled by enzymes – these are destroyed at temperatures above 400C
2. Carbon dioxide
Photosynthesis increases at first but is then limited by a lack of increase in temp or light
3. Light
Photosynthesis increases at first but is then limited by a lack of increase in temp or CO2

17. Encouraging Photosynthesis
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Using knowledge of limiting factors, explain how plant growth is encouraged in a greenhouse:

18. Photosynthesis and Respiration
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In earlier work we looked at respiration:
Glucose oxygen water carbon dioxide
Photosynthesis is the reverse of respiration:
Water carbon dioxide glucose oxygen

19. Gas concentrations over 24 hours
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Midnight
Midday
Concentration of gas around plant
Oxygen
Carbon dioxide

20. B4c: Leaves and Photosynthesis
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B4c: Leaves and Photosynthesis

21. Packed with chloroplasts
Structure of the Leaf
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How do each of the following features help photosynthesis?
Large surface area
Lots of chlorophyll
Transparent
Thin structure
Packed with chloroplasts
Network of veins
Lots of air spaces
Holes

22. B4d: Diffusion and Osmosis
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B4d: Diffusion and Osmosis

23. Oxygen passes into cells by diffusion
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Diffusion is when something travels from an area of high concentration to an area of low concentration. For example, consider the scent from a hamburger…
The “scent particles” from this hamburger are in high concentration here:
Eventually they will “diffuse” out into this area of low concentration:
Oxygen passes into cells by diffusion

24. Words – faster, low, gradient, temperature, energy
Diffusion Summary
04/02/2019
Diffusion is when particles spread from an area of high concentration to an area of ___ concentration. The particles move along a “concentration _____” and this process takes no _____. Diffusion can be accelerated by increasing the _______ of the particles, which makes them move _______, or by increasing the surface area of the membrane.
Words – faster, low, gradient, temperature, energy

25. Words – membrane, concentrated, dilute, diffusion, gradient
Osmosis
04/02/2019
Osmosis is a “special kind of ___________”. It’s when water diffuses from a __________ area to a less concentrated area through a partially permeable _________ (i.e. one that allows water to move through but not anything else):
Water
Sugar solution
In this example the water molecules will move from left to right (along the concentration ______) and gradually _____ the sugar solution.
Words – membrane, concentrated, dilute, diffusion, gradient

26. Strong sugar solution Medium sugar solution Potato cells
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Strong sugar solution
Medium sugar solution
Potato cells
Weak sugar solution

27. Osmosis of water from leaves
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High conc. of water
Low conc. of water
Water leaves the plant by diffusing through osmosis into the air spaces and then evaporating.

28. Words: out, swollen, higher, soil, osmosis, open
Turgor pressure
04/02/2019
Consider a plant that’s been well watered:
Because there is a _______ concentration of water in the soil than in the ____, water will enter the plant cells through _______ and the cells will become TURGID (“_________”):
In this case the stomata will ______ to allow carbon dioxide in and water ___ and photosynthesis will carry on. The cell wall prevents the cell from bursting.
Words: out, swollen, higher, soil, osmosis, open

29. Turgid = “tense” Flaccid = “floppy”
Turgor pressure
04/02/2019
Consider a plant that’s been badly watered:
Because there is a lower concentration of water in the soil than in the plant water will leave the plant cells through osmosis and the cells will become FLACCID (“soft”):
In this case the stomata will close to stop water from escaping through transpiration. Because they are closed carbon dioxide cannot get in and so photosynthesis stops. The cell looks like a deflated balloon – this is called “plasmolysis”.
Turgid = “tense” Flaccid = “floppy”

30. Osmosis in Animal Cells
04/02/2019
Animal cells don’t have a cell wall so if red blood cells are placed in a weaker solution they swell up, whereas if they are put in a more concentrated solution they will shrivel.
If they absorb enough water they will eventually burst (“lysis”), whereas if they lose enough water they shrivel up and become “crenated”. These differences to plant cells are caused by the lack of cell wall.

31. B4e: Transport in Plants
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B4e: Transport in Plants

32. Using water Plants need water to do the following: Produce glucose
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Plants need water to do the following:
Produce glucose
Enable transport of minerals
Form fruits
Enable growth
Keep the leaves cool

33. Close up on the stem - Xylem and Phloem
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Xylem vessels are made from dead plant cells and are used by the plant to transport water and soluble mineral salts from the roots to the stem and the leaves.
Phloem are tubes made from long columns of living cells and are used by the plant to transport dissolved food to the whole plant for respiration and storage.

34. Transpiration 1) Water evaporates through the stomata
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1) Water evaporates through the stomata
2) Water passes back into the leaf through the XYLEM vessels by osmosis
3) Water is then pulled upwards through the xylem tissue
4) This is replaced by water entering from the root tissue
5) Water enters root hair cells by osmosis to eventually replace the water lost through respiration

35. Factors affecting transpiration
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1) High light intensity
This causes the stomata to open thereby increasing the rate of water loss.
2) High temperatures
This increases the speed of molecule movement and so speeds up transpiration.
3) Increased wind
This will blow the molecules away and so speeds up transpiration.
4) High humidity
This decreases the concentration gradient and so slows transpiration down.

36. Measuring Transpiration
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The rate of transpiration can be measured using a “potometer”.
Bung to prevent evaporation
As the plant takes up water the rate can be measured by determining the speed of the bubble.

37. Water loss
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Water loss through the stomata is biggest on a hot, dry, windy day. Plants that live in these conditions often have a thicker waxy layer.

38. Water loss through leaves
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Carbon dioxide enters a leaf through the ________. These cells are also responsible for controlling the ______ content of the ____…
The ______ cells control how wide the stomata opens (if at all). If too much water is being lost through the stomata then the guard cells will _____ to prevent further loss.
Water and carbon dioxide enter here
No more water and carbon dioxide allowed in
Words – water, close, stomata, guard, leaf

39. B4f: Plants need Minerals
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B4f: Plants need Minerals

40. Essential Minerals Nitrates: Magnesium: Phosphates: Potassium:
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Nitrates:
Used to make amino acids to form proteins
Lack of it leads to stunted growth
Magnesium:
Used to make chlorophyll for photosynthesis
Lack of it leads to yellow leaves
Phosphates:
Used to make DNA and cell membranes
Lack of it leads to underdeveloped roots and discoloured leaves
Potassium:
Used to make enzymes for respiration and photosynthesis
Lack of it leads to underdeveloped fruit and flowers

41. Words – active, concentration, ions, higher, energy
Active Transport
04/02/2019
Here is a root hair cell:
Now consider the concentration of minerals around the cell:
Less concentrated
Mineral
More concentrated
Plants need minerals and ____ and these are “taken up” by the root hair cell. The _________ of these minerals inside the cell is ______ than outside so _____ is needed for the process. This process is called _______ transport.
Words – active, concentration, ions, higher, energy

42. 04/02/2019
B4g: Decay

43. Recycling ourselves Eating Waste Death Absorption Broken down
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04/02/2019
Eating
Waste
Death
Absorption
Broken down
Microbes are the key to this – they break down waste and dead bodies so that the products can be used by plants for growth. Microbes work best in warm, moist conditions where there is plenty of oxygen.

44. Words – more, moist, simpler, growth, denatured
More about Decay
04/02/2019
Decay is the process of breaking down complex structures into ______ ones. This is done be micro organisms.
The rate of decay is affected by the _______ of these microorganisms:
Temperature – the micro organisms’ rates of growth and respiration are quickest at around 40OC. They become “_________” at temperatures higher than this.
Oxygen – more oxygen means _____ micro organisms.
Water – micro organisms grow quickest in ______ conditions.
Words – more, moist, simpler, growth, denatured

45. Decomposers
04/02/2019
Microorganisms are called “decomposers”. They are used by humans to help the decay process in compost heaps and sewage treatment works.
They are helped by earthworms, woodlice and maggots. These are called “detritivores” – this means they feed on dead organisms and waste and break it down (i.e. increase the surface area) to speed up the decay process.

46. Saprophytes
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A “saprophyte” is an organism like the shiitake mushroom that digests dead material like dead wood:
This mushroom digests dead wood using “extra-cellular digestion”, i.e. the food is digested outside of the cell membrane, often by having enzymes excreted onto it.

47. Preventing Food Decay
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Food can be preserved by limiting the growth of micro organisms. Some examples:
Using sterile tins/bottle/cans
2) Using a fridge or freezer
3) Pickling the food
4) Adding sugar or salt
5) Dehydrating the food

48. 04/02/2019
B4h: Farming

49. Pests
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Crops can be damaged by pests such as herbivorous insects, weeds and fungal infections. How can the problem be reduced?
1) Using ________ – these will kill _____ but they can build up in plants causing the death of other _______.
2) Introducing natural predators, such as ______ – not as easy as using pesticides and would take _______.
Words – ladybirds, animals, insects, longer, pesticides

50. Biological pest control
04/02/2019
Sometimes a food web can be controlled by the introduction of a pest, e.g.
Ladybirds feed on aphids
A wasp looking for caterpillar larvae
What are the advantages and disadvantages of using pests?

51. Accumulation of pesticides
04/02/2019
Insecticides can wash into a stream or lake where they are taken up by microscopic water plants. Consider the food chain:
Although the level of insecticides in the plants is small, it will build up through the food chain due to the number of organisms in each stage. In this example, if each plant had “one bit” of pesticide, the bird will have eaten 9 bits.

52. Intensive Farming Some examples of intensive farming: Fish farms
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Some examples of intensive farming:
Fish farms
Battery farms
Glass houses
Hydroponics

53. Farming Methods
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There are basically two types of farming method; “intensive” and “organic”:
Intensive
Organic
Cost
Produce
Fertilisers
Space
Labour done by...

54. Intensive Farming
04/02/2019
Intensive farming can be used to improve the efficiency of energy transfer in a food chain by two ways:
1) Get rid of energy transfer to pests or competing weeds
2) Limit an animal’s movement or keep it warm:

55. Hydroponics Hydroponics basically means “growing plants without soil”.
04/02/2019
Hydroponics basically means “growing plants without soil”.
Advantages
Disadvantages
Mineral levels can be controlled
Plants have to be supported
Reduced risk of disease
Expensive fertilisers