1. B2 Topics- What do you want to revise?
Plant and Animal Cells
Specialised Cells
Bacterial and Fungal Cells
Diffusion
Animal Tissues, Organs and Organ Systems
Photosynthesis
Plant Tissues and Organs
Sampling Techniques
Mean, mode median
Enzymes
Respiration
Mitosis
Meiosis
Inheritance
Mendel
Genetic diseases
Embryo Screening, Stem Cells and DNA Fingerprinting
Fossil record
Extinction
Forming a New Species

2. Animal and Plant Cells

3. In Both Animal and Plant Cells
Part
Function
nucleus
contains genetic material, which controls the activities of the cell
cytoplasm
most chemical processes take place here, controlled by enzymes
cell membrane
controls the movement of substances into and out of the cell
mitochondria
most energy is released by respiration here
ribosomes
protein synthesis happens here
Plant Cells Only
Part
Function
cell wall
strengthens the cell
chloroplasts
contain chlorophyll, which absorbs light energy for photosynthesis
permanent vacuole
filled with cell sap to help keep the cell turgid

4. Specialised Cells
You are likely to be given information, perhaps in a diagram, to help you to explain the adaptations of a particular cell type to its function.
You should be able to name specialised cells, state their function and explain how they are adapted to carry out their function

5. Red Blood Cells Carry Oxygen to the Cells Adaptations
Thin outer membrane, to allow quick diffusion of oxygen
Large surface area, to allow diffusion quicker
No nucleus, so whole cell is full of haemoglobin

6. Sperm Cell Fertilises the female egg cell Adaptations
The head contains genetic information and an enzyme to help penetrate the egg cell membrane.
The middle section is packed with mitochondria for energy.
The tail moves the sperm to the egg.

7. Root Hair Cell Absorbs water and mineral ions from the soil
Adaptations
Long 'finger-like' process with very thin wall, which gives a large surface area.

8. Palisade Cell Absorbs light energy for photosynthesis Adaptations
Packed with chloroplasts.
Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.

9. Bacterial and Fungal Cells

10. Bacteria A bacterium is a single-celled organism.
It has cytoplasm, a membrane and a surrounding cell wall, but the genetic material in a bacterial cell is not in a distinct nucleus.

11. Fungi Yeast is a single-celled organism.
Like bacterial cells, yeast cells have cytoplasm and a membrane surrounded by a cell wall.
Unlike bacterial cells, yeast cells have a nucleus.

12. Diffusion

13. Key Points From a high concentration to a low concentration
If answering about movement through cells, you must say “through a cell membrane” or “through a partially permeable membrane”

14. Two examples of diffusion down concentration gradients
Location
Particles move
From To
Small intestine
Digested food products
Blood in capillary of villus
Lungs
Oxygen
Alveolar air space
Blood circulating around the lungs

15. Animal Tissues and Organs
Cells are the basic units of life.
Groups of cells work together to form tissues.
Groups of tissues work together to form organs.

16. The liver produces bile. The bile is stored in the gall bladder.
Digestive System
The liver produces bile. The bile is stored in the gall bladder.
After the stomach, food travels to the small intestine. Enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. Bile is an alkaline it is secreted into the small intestine, where it emulsifies fats. This is important, because it provides a larger surface area in which the lipases can work.
The pancreas secretes enzymes but food does not travel through the pancreas so don’t state it as a “site of digestion”

17. Plant Tissues

18. Tissue
Function
Epidermal tissue
Covers the plant
Palisade Mesophyll
Carries out photosynthesis
Xylem and phloem
Transport of substances around the plant
Stomata
To allow CO2 to diffuse into the leaf

19. Photosynthesis Examples of plant organs include:
Roots
Stems
Leaves- site of photosynthesis
Factors that can limit the rate of photosynthesis;
CO2 concentration
Light intensity
Water availability
Temperature

20. Light Intensity
Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.
Can you explain what is happening here?

21. CO2
Something other than CO2 concentration is acting as a limiting factor
Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

22. Temperature
If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. Why?

23. Respiration
Site of respiration- mitochondria

24. Aerobic- “in the presence of oxygen”
Glucose + oxygen  Carbon Dioxide water (+Energy)
C6H12O6+O2  CO2 + H2O (+energy)
The energy made is used to make larger molecules from smaller molecules.
It is also used in muscle contraction and maintaining body temperature.
Good for long distance.

25. Anaerobic Respiration- no oxygen
Remember in yeast anaerobic respiration produces ethanol and carbon dioxide (which is why we used it to make beer and bread)
Anaerobic Respiration- no oxygen
Glucose → Lactic acid (+ energy) This type of respiration may be used when, for example, an animal is being chased by a predator (short bursts). Less energy is produced less than from aerobic respiration.

26. Sampling Techniques- Quadrats
A square made of wire. It may contain further wires to mark off smaller areas inside. The organisms underneath, usually plants, can be identified and counted.

27. Quadrat Key Points
Random sampling can be achieved by assigning numbers to the area being sampled and using a random number generator
It should be placed randomly so that a representative sample is taken
The validity and reproducibility of the results increases as the results from more quadrats are analysed

28. Transects
Transects can be used together with quadrats to create a belt transect.
A transect is a line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground.
The number of organisms of each species can be observed and recorded at regular intervals along the transect.

29. Number of dandelion plants
Mean
Add the numbers together and divide the total by the amount of numbers
Example
Mean = ( ) ÷ 5 = 18 ÷ 5 = 3.6
Quadrat sample
Number of dandelion plants 1 2 4 3 5

30. Mode The median is the middle number. To calculate a median:
Put all the numbers in numerical order
If there is an odd number of results, the median is the middle number
If there is an even number of results, the median will be the mean of the two middle numbers
Example :
The median is 4.

31. Median
The mode is the number which occurs most often in a set of data.
Example :
The number 5 occurs twice, so it is the mode.
(Note that you can have more than one mode.)

32. Enzymes- biological catalysts (speed up reactions)

33. When the enzyme and substrate are together this is called an enzyme-substrate complex

34. Key Points Enzymes are reusable
They are affected by pH and temperature- these can cause them to denature
They are proteins (made by ribosomes)
Enzymes have an optimum temperature and pH (faster rate of reaction)

35. Enzymes and Temperature
Describing the changes; The rate of reaction increases up to 40°c. The optimum is 40°c. After 40°c the rate of reaction decreases to 0 at approximately 63°c.

36. Explaining the changes;
At 0°c the rate of reaction is slow, this is because there is a small amount of kinetic energy and the number of successful collisions between the enzymes active site and the substrate are low. After 40°c the enzymes start to denature and are no longer complimentary to the substrate.

37. pH and enzymes Different enzymes have different optimum temperatures.
Above or below the optimum the enzymes denature.

38. Enzymes are specific and complimentary to their substrates
Reaction catalysed
Where the enzyme is produced
Amylase
Starch    →    Glucose
salivary glands, pancreas, small intestine
Protease
Proteins    →    Amino acids
stomach, pancreas, small intestine
Lipase
Lipids    →  Fatty acids +
Glycerol
pancreas, small intestine

39. Enzymes in Industry
Remember when talking about enzymes you should describe the reactants and the products.
When lipase breaks down fats, fatty acids will lower the pH
Enzyme
Use
Protease
Pre-digest proteins during the manufacture of baby foods
Lipase
Together with protease - in biological detergents to break down - digest - the substances in stains into smaller, water soluble substances
Carbohydrase
Convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinks
Isomerase
Convert glucose syrup into fructose syrup - fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods

40. Mitosis Parent cell Chromosomes make identical copies of themselves
They line up along the centre
They move apart
Two daughter cells form with identical chromosomes to the parent cell (46 chromosomes)

41. Meiosis Creates 4 daughter cells Genetically unique
Gametes (sperm and egg cell)
23 chromosomes

42. Inheritance Vocabulary
Alleles -different forms of the same gene
Homozygous- 2 of the same allele e.g. bb
Heterozygous- 2 different versions of the same gene e.g. Bb
Genotype- the genes present
Phenotype- the genes that are expressed e.g. Bb, brown eyes
Recessive- only expressed when homozygous
Dominant- expressed when either heterozygous or homozygous

43. Mendel
Gregor Mendel ( ) studied the inheritance of different characteristics in pea plants
He was the first person to come up with the idea that “factors” are passed on through generations and sometimes they skip a generation (recessive genes)

44. Generation 1

45. Generation 2

46. Cystic Fibrosis
Affects the cell membranes, causing the production of thick and sticky mucus. It is caused by a recessive allele.

47. Punnett Square

48. Polydactyly
Polydactyly is an dominant inherited condition in which a person has extra fingers or toes.
This means it can be passed on by just one parent if they have the disorder.

49. DNA fingerprinting
By cutting a sample of DNA into fragments and comparing it with other samples it's possible to work out if the DNA has come from the same person.

50. Embryo Screening
Embryos can be screened for the alleles that cause polydactyly, cystic fibrosis and other genetic disorders.
Note that you do not need to know or understand how embryo screening works for the examination but your need to be able to discuss the pros and cons

51. Discussing Ethical Issues
Science can answer the question, 'What are the chances of my child having cystic fibrosis?'. However, it cannot answer the question, 'Should I have my pregnancy terminated?‘
Clearly state the issue
Summarise the different views
Identify arguments that are based on the right decision, ie a decision that produces the best outcome for most of the people involved.
Identify when certain actions are very hard to justify because they are considered unnatural or wrong.

52. Stem Cells
Human stem cells can come from human embryos or from adult bone marrow.
They are able to develop into any kind of human cell.
Note that you do not need to know any details of how this happens for the examination.
They have the potential to be used in new treatments for conditions such as Parkinson's disease and paralysis.
There are social and ethical issues concerning the use of human embryonic stem cells in medical research and treatments.

53. Fossil Record
Fossil remains have been found in rocks of all ages. Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks. This supports the theory of evolution.
Many early forms of life were soft-bodied - and have left few traces behind.

54. Forming a New Species
New species can arise as a result of isolation. This is where two populations of a species become geographically separated.
Genetic variation - where each population has a wide range of alleles that control their characteristics
Natural selection - where the alleles which help an organism to survive are selected in each population
Speciation - where the populations become so different that successful interbreeding cannot happen anymore

55. Extinction
Some of the factors that can cause a species to become extinct:
New diseases
New predators
New, more successful competitors
Changes to the environment over geological time - such as a change in climate
A single catastrophic event - such as a massive volcanic eruption or a collision between an asteroid and the Earth