Biology B4 - B6

Question 1

The Carbon Cycle

Answer 1

1) There’s only one arrow going down from CO2 in the air. The whole thing is ‘powered’ by photosynthesis. Green plants use the carbon from CO2 in the air to make carbohydrates, fats and proteins
2) Eating passes the carbon compounds in the plant along to animals in a food chain or web
3) Both plant and animal respiration while the organisms are alive releases CO2 back into the air
4) Plants and animals eventually die and decompose, or are killed and turned into useful products
5) When plants and animals decompose they’re broken down by microorganisms, such as bacteria and fungi. These decomposers release CO2 back into the air by respiration, as they break down the material
6) Some useful plant and animal products, e.g. wood and fossil fuels, are burned (combustion)
This also releases CO2 back into the air
7) Decomposition of materials means that habitats can be maintained for the organisms that live there, e.g. nutrients are returned to the soil and waste material, such as dead leaves, doesn’t just pile up

Question 2

The Nitrogen Cycle and the Water Cycle: 4 Bacteria

Answer 2

Decomposers - Decompose proteins and urea and turn them into ammonia, which goes on to form ammonium ions

Nitrifying Bacteria - turn ammonium ions in decaying matter into nitrates

Nitrogen-Fixing bacteria - Turns atmospheric N2 into nitrogen compounds that plants can use

Denitrifying Bacteria - turns nitrates back into N2 gas. This is of no benefit to living organisms. Denitrifying bacteria are often found in waterlogged soils

Question 3

Decomposition

Answer 3

Microorganisms help recycle materials through decomposition.

The main types of decomposers are bacteria and fungi

Question 4

What factors affect the rate of decomposition?

Answer 4

Oxygen availability - Many decomposers respire aerobically

Temperature - They contain enzymes which have optimum temperatures

Water Content - Decomposers need water to survive

Question 5

4 levels of organisation within an ecosystem

Answer 5

Individual - A single organism
Population - All the organisms of one species in a habitat
Community - All the organisms (different species) living in a habitat
Ecosystem - A community of organisms along with all the non-living (abiotic) conditions

Question 6

Abiotic Factors that affect communities

Answer 6

Temperature
Moisture level
Light intensity
pH of soil

Question 7

Biotic factors that affect communities

Answer 7

Availability of food

Number of predators

Question 8

Parasites and mutualistic relationships

Answer 8

A mutualistic relationship is where two organisms depend on each other, benefitting them both.

Parasites live off a host. They take what they need to survive without giving anything back. This often harms the host.

Clownfish live among the poisonous tentacles of sea anemones. They are the only fish that can survive the toxins so they are protected from their predators. In return, the clown fish eat the parasites that could harm the anemones.

Question 9

Food Chains and Food Webs

Answer 9

Food chains show what’s eaten by what in an ecosystem.

Producers –> Primary consumers –> Secondary Consumers –> Tertiary consumers

They all eventually get eaten by decomposers

Each of these levels are called trophic levels

Food Webs show how food chains are linked.

Question 10

Pyramids of Biomass and Number

Answer 10

Pyramids of biomass just show the mass of living material at that stage of the food chain

Pyramids of numbers can be different shapes and show the amount of organisms on each trophic level

Question 11

Biomass transfer

Answer 11

Efficiency = biomass available in the next level / biomass that was available to previous level

Question 12

Genes and variation

Answer 12

The genome is the entire genetic material of an organism
The genetic material is stored in the nucleus and is arranged into chromosomes
Each chromosome is a very long molecule of DNA that has been coiled up.
A gene is a short length of a chromosomes
They code for certain proteins

Organisms of the same species have differences

Question 13

Genetic Variants

Answer 13

Mutations are changes to the genome and are quite rare, usually inherited. This means that the sequence of the DNA bases in the gene is changed, which produces a genetic variant.
Some variants have a small influence on the organism’s phenotype - such as eye colour
Very occasionally, variants can have such a dramatic effect that they determine phenotype - Cystic Fibrosis can be caused by the deletion of just three bases but it has a huge effect on phenotype.

Variants can affect coding and non-coding DNA

Mutations in non-coding DNA can affect how genes are expressed - whether or not genes are ‘switched on’. They can stop the transcription of mRNA so the protein coded for by that gene is not produced at all

Question 14

Sexual Reproduction

Answer 14

Sexual Reproduction produces genetically different cells. Genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.

In sexual reproduction, the parents produces gametes which are haploid cells; they only contain half the number of chromosomes of normal cells.

Question 15

Meiosis

Answer 15

1) Before the cell starts to divide, it duplicates its DNA (so there’s enough for each new cell). One arm of each X-Shaped chromosome is an exact copy of the other arm

2) In the first division in meiosis, the chromosomes lines up in pairs in the centre of the cell.
One chromosome in each pair came from the organism’s mother and one came from its father

3) The pairs are then pulled apart so each new cell only has one copy of each chromosome.
4) Each new cell will have a mixture of the mother’s and father’s chromosomes. Mixing up the genes like this is really important - it causes genetic variation
5) In the second division, the chromosomes line up again in the centre of the cell. It’s a lot like mitosis. The arms of the chromosomes are pulled apart
6) You get four haploid gametes - each only has a single set of chromosomes. The gametes are all genetically different.

Question 16

Asexual Reproduction vs Sexual Reproduction

Answer 16

Asexual reproduction:
Lots of offspring can be produced quickly and only one parent is needed, so they can reproduce whenever they need to.
However, there is no genetic variation, so if one gets ill then the rest can too

Sexual reproduction:
Creates genetic variation within the population, increasing the chances of the survival. However, it takes quite a long time and two parents are needed, producing less offspring and more time/energy.

Question 17

Genetic Diagrams and Alleles

Answer 17

Most of the time, you have two copies of each gene (two alleles) - one from each parents
If alleles are different, you have instructions for two different version of a characteristics, but you only show one version. The characteristic that appears is caused by the dominant allele and the other is said to be recessive.

If you’re homozygous for a train you have two alleles the same for that particular gene (CC or cc)

If you’re heterozygous for a trait you have two different alleles for that particular gene (Cc)

Question 18

Sex Chromosomes

Answer 18

Your chromosomes control whether you’re male or female.
There are 23 pairs of chromosomes in every human body cell. The 23rd air are labelled XY. These are sexy chromosomes - they decide whether you turn out male of female

Males have an X and Y chromosomes: XY
The Y chromosomes cause male characteristics
Females have two X chromosomes: XX
The lack of a Y chromosome causes female characteristics

Like other characteristics, sex is determined by a gene.
The Y chromosome carries a gene which makes an embryo develop into a male as it grows. Females who always have two X chromosomes, don’t have this gene and so they develop in a different way.

Question 19

Gregor Mendel

Answer 19

Mendel crossed a tall pea plant (TT) with a dwarf pea plant (tt). All offspring were tall (Tt)
So Mendel took two of the tall plants from the first set of offspring and crossed them. This time, 75% of the offspring were tall but 25% were draw plants

Question 20

Artificial Classification

Answer 20

Early classification systems only used observable features to place organisms into groups
Artificial classification systems are still used to make keys

Question 21

Natural Classification

Answer 21

Natural classification systems use evolutionary relationships. They use information about organisms’ common ancestors and about their common structural features to sort organisms

In natural classification systems, living things are divided into five kingdoms - Animal, plant, fungi, protist and moneran
The kingdoms are then subdivided into smaller and smaller groups - Phylum, class, order, family, genus, species. The hierarchy ends with species - the groups that contain only one type of organism. A species is defined as a group of similar organisms that are able to reproduce to give fertile offspring

Question 22

Natural Selection

Answer 22

Natural Selection increases advantageous Phenotypes. Due to genetic variation, there is a chance that DNA can mutate and variants are created. These variants may possess a trait that is advantageous in the environment they live in. For example, a mutation may occur in a bird so they can break the shells of their food easily

Question 23

Evolution

Answer 23

Evolution is the change in inherited characteristics of a population over time, through the process of natural selection.
This may allow them to live a better life in their environemnt

Question 24

Investigating Distribution and Abundance

Answer 24

Pooters are for collecting Ground Insects
Pitfall traps are another way to investigate ground insects or small animals
A sweep net is used for collecting insects, spiders, etc. from long grass
A pond net is used for collecting insects, water snails, etc. from ponds and rivers

A quadrat is used to study the distribution of small organisms.
The population sized can be estimated by multiplying the mean number of an organism per m^2 by the total area of the area.

You can also calculate population using capture-recapture
Population size = number in first sample x number in second sample / number in second sample previously marked

Keys are used to identify this

Question 25

Factors affecting Distribution

Answer 25

Abiotic factors - Temperature - Use a thermometer
Moisture level - Soil Moisture meter
Light intensity - Light Sensor
Soil pH - indicator liquid. Water is added to a soil sample and then an indicator liquid is added that changes colour depending on the pH

Biotic Factors - Competition

Question 26

Selective Breeding

Answer 26

Organisms are selectively bred to develop the best features according to what we want from them

Question 27

Genetic Engineering

Answer 27

1) The DNA you want to insert is cut out with a restriction enzyme
Restriction enzymes recognise specific sequences of DNA and cut the DNA at these points
2) The plasmid is then cut open using the same restriction enzymes
3) This creates sticky ends on the DNA - short tails of unpaired bases that are complementary to each other
4) The plasmid and the DNA you’re inserting are mixed together with the ligase enzymes
5) The ligase join the sticky ends of the two pieces of DNA together
6) Plasmid vectors that contain the new DNA are inserted into other cells, known as hosts. THe host cells can now use the gene you inserted to produce the desired characteristics.

Question 28

Diseases

Answer 28

A pathogen is a type of microorganism that causes disease. Types of pathogen include bacteria, viruses, protists and fungi

A communicable disease is a disease that can spread between organisms

Non-communicable disease cannot be passed from one organism to another

Question 29

HIV

Answer 29

HIV stops the immune system from working properly
The bacteria that cause another communicable disease called tuberculosis are normally destroyed by the immune system before symptoms of the disease can develop
But if the tuberculosis bacteria infect someone with HIV, the bacteria are not destroyed by the immune system so the disease progresses very rapidly

Question 30

How are communicable diseases transmitted

Answer 30

Water, air, contact, body fluids, animal vectors, soil and food

Question 31

The Human Immune System

Answer 31

Your immune system can attack pathogens.
The most important part of your immune system is the white blood cells. They travel around in your blood and crawl into every part of you, constantly patrolling for pathogens. When they come across an invading pathogen, they have three lines of attack:

1) Consuming them
Some white blood cells (phagocytes) have a flexible membrane and contain lots of enzymes. This enables them to engulf foreign cells and digest them. This is called phagocytosis

2) Producing antibodies
Every invading pathogen has unique antigens on its surface
When your white blood cells come across a foreign antigen they will start to produce proteins called anti bodies to lock onto the invading cells. The antibodies produced are specific to that type of antigen - they won’t lock on to any others
Some white blood cells, called memory cells, stay around in the blood after the pathogen has been fought off. If the person is infected with the same pathogen again, the white blood cells will rapidly produce the antibodies to help destroy it - the person is naturally immune now

3) Producing antitoxins
These counteract toxins produced by invading bacteria

Question 32

Vaccines

Answer 32

Vaccination involves injecting dead, inactive or weakened pathogens into the body. These carry antigens, so even though they’re harmless they still trigger an immune response - your white blood cells produce antibodies to attack them. The memory cells stay in the blood so the next time the same pathogen enters the body, it can react instantly, making the person immune.

Question 33

Medicines used to treat disease

Answer 33

Antibiotics kill bacteria without killing your own body cells

Antivirals can be used to treat viral infections

Antiseptics are chemicals that destroy microorganisms or stop them growing

Question 34

Ways of increasing Agricultural yields

Answer 34

Fertilisers are used to ensure crops have enough nutrients. Plants need certain elements, such as nitrogen, so they can make important compounds like proteins. If plants don’t get enough of these, then fertilisers are used to increase crop yield.

Pest Control can also help in this
Pesticides are a form of chemical pest control which are sprayed onto crops to kill the pests that damage them.

Biological control is an alternative to using pesticides. It involved using other organisms to reduce the number of pests. However, this could cause problems in the ecosystem. No chemicals are used, meaning it’s less harmful

Question 35

Hydroponics

Answer 35

Hydroponics is where plants are grown without soil. Instead, nutrient solutions are used. You can picture them as lab plants.

Glasshouse tomatoes and other salad crops are grown with hydroponics on a commercial scale in places where they are unable to grow.

However, a lot of fertiliser is required. This means that it could be potentially harmful and expensive.

Question 36

Genetic modification in plants

Answer 36

Genetically modified (GM) crops are crop plants that have had their genes modified. They can made to be:

• Insect resistant
• Virus resistant
• Herbicide resistant

Example:
Plum trees have been genetically modified to be resistant to the plum pox virus

Question 37

Selective breeding - What features do we look for?

Answer 37

• Maximum yield of meat, milk, grain, etc. - best food produced, which is very important for food security
• Good health and disease resistance
• In animals, other qualities like temperament, speed, fertility, good mothering skills, etc
• In plants, other qualities like attractive flowers, nice smell, etc.

Question 38

Drawbacks of selective breeding

Answer 38

The main drawback is a reduction in the gene pool - the number of different alleles in a population. This is because the farmer keeps breeding from the “best” animals or plants - which are all closely related. This is known as inbreeding

Inbreeding can cause health problems because there’s more chance of the organisms developing harmful genetic disorders when the gene pool is limited

If a new disease appears, there’s not too much variation so they all may die out

Question 39

Aseptic

Answer 39

Antiseptics are chemicals that destroy microorganisms or stop them growing
Antiseptics are used outside the body to help to cleans wounds and surfaces. They’re used to prevent infection rather than treat it
Plenty of household products contain antiseptics
Antiseptics are using in hospitals and surgeries to prevent the spread of infections of MRSA

Question 40

Antiseptic Technique - Culturing organisms

Answer 40

Contamination by unwanted microorganisms will affect your results and can potentially result in the growth of pathogens. To avoid this:

• Regularly disinfect work surfaces
• Sterilise all glassware and other equipment, such as forceps, before and after use
• If an inoculation loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame
• Work near a Bunsen flame. Hot air rises, so microbes in the air should be drawn away from the culture
• Briefly flame the neck of the glass container of bacteria just after it’s opened and just before it’s closed