Additional Biology (B2)

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Cells and Simple Cell Transport

Diffusion occurs when gas particles spread out or when particles in a dissolved solution spread out.

Particles move from an area of high concentration to an area of low concentration.

They diffuse down the concentration gradient.

The greater the concentration gradient, the faster the process.

Diffusion allows oxygen to move from the blood vessels into the cells.

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Animal and Plant Cells

Nucleus: Contains genetic material - Control cell activities.

Cytoplasm: Where chemical processes take place - Controlled by enzymes.

Cell Membrane: Controls movement of substances into/out of cell.

Mitochondria: Energy is released by respiration here.

Ribosomes: Protein Synthesis - Make proteins from amino acids.

Plant Cells Only

Cell Wall: Strengthens the cell

Chloroplasts: Contain chlorophyll - Absorbs light energy for photosynthesis.

Permanent (sap) Vacuole: Filled with cell sap to keep cell turgid.

* Bacteria: Single-celled organism. Contains: Cytoplasm, Cell Membrane, Cell Wall, No Nucleus.

* Yeast: Single-celled. Contains: Cytoplasm, Cell Membrane, Cell Wall, Nucleus.

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Specialised Cells

> Leaf Cell - Absorbs light energy for photosynthesis. Filled with chloroplasts. Cells form a continuous layer to efficiently absorb more light.

> Root Hair Cell - Absorbs water and mineral ions from the soil. Hair like structure to increase surface area.

> Sperm Cell - The head contains genetic information and an enzyme to help penetrate the egg cell's membrane. A tail to swim to the egg / Mitochondria for energy.

> Red Blood Cell - Contains haemoglobin to carry oxygen to the cells.

Thin outer membrane = Oxygen diffuses through easily. Shape increases surface area to allow more oxygen to be absorbed efficiently. No nucleus = More space to carry haemoglobin.

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Organs in Animals

Living things = Multicelular - The cells work together.

Cells --> Tissues --> Organs --> Organ Systems

Muscle Cells: Contract - Allows movement

Epithelia Cells: Cover surfaces for protection

Glandular Tissue: Produces enzymes and hormones

The Stomach

- Muscular Tissue --> Churn/mix food and other contents of the stomach

- Epithelial Tissue --> Covers inner and outer surfaces of the stomach

- Glandular Tissue --> Produces digestive juices (acid and enzymes)

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The Digestive System

- Pancreas and Salivary Glands --> Produce digestive juices

- Stomach --> Digests food (Mixes food with acid/enzymes)

- Liver --> Produces bile

- Small Intestine --> Digests/absorbs soluble foods

- Large Intestine --> Absorbs water from undigested food,             produces faeces.

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Plant Organs

> Roots: Absorb water and minerals from the soil

> Stem: Transports minerals around the plant

> Leaves: Main organ for photosynthesis


* Epidermal Tissue - Covers the plant

* Mesophyll - Carries out photosynthesis

* Xylem - Transports minerals around the plant.

* Phloem - Transports products of photosynthesis

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- Chlorophyll - Absorb sunlight

- Large Surface Area - Absorb more light

- Stomata - Let CO2 diffuse into the leaf. Thin - Short distance for CO2 to diffuse.

- Network of Veins - Support the leaf and Transport carbohydrates

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> CO2 + H2O -----(light energy)-----> C6H12O6 + O2

Plants need Nitrate ions to produce proteins.

Light energy is absorbed by chlorophyll (green substance).

Some glucose is used for respiration, whilst some is converted into insoluble starch for storage. This can be turned back to glucose and used in respiration.

Limiting Factors:

- Lack of Light: Light provides the energy needed for the process.

- Too little CO2 (sometimes in an enclosed space, e.g. greenhouse).

- Too low Temperatures: Enzymes don't work effectively.

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Organisms in Their Environment

The distribution of organisms is affected by environmental factors.

Animals as well as plants are affected by physical factors.

Physical factors

* Temperature

* Light

* Availability of Water

* Availability of Nutrients

* Availability of Oxygen and Carbon Dioxide

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Collecting Quantitative Data

> Transects - A line across a habitat or part of a habitat.

> Quadrat - A square made of metal or wood, subdivided into a grid.

A quadrat is used to estimate the population of an organism in a habitat

Collecting Data:

- Quadrat: Placed randomly, or at equal intervals

- Transect: Not random - Line is marked between two points.

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Proteins and Enzymes

Proteins are made of long chains of amino acids.

Proteins can be muscle, hormones, antibodies, catalysts, etc.

An enzyme is a type of protein.

Enzymes are biological catalysts.

Proteins are polymers, made up of amino acid monomers.

If the shape of an enzyme changes, we say it has been Denatured.

Facors Affecting Enzymes

- High temperature denature enzymes.

- Changes in pH can denature enzymes as different enzymes work best at different pH values.

l---> e.g. Intestinal Enzyme = Optimum pH of 7.5, Stomach Enzyme = Optimum pH of 2.

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Enzymes in Digestion

Enzymes catalyse digestive reactions to break down the natural polymers found in food.

In digestion, large molecules from food are broken down into smaller, soluble ones.

Digestive enzymes are produced by specialised cells in glands and in the lining of the gut.

The enzymes pass out of the gut and come into contact with the food.

Digestive enzymes work outside of the cells that produce them.

* Amylase - Produced in the Salivary Glands, Pancreas and Small Intestine. STARCH -> GLUCOSE

* Protease - Produced in the Stomach, Pancreas and Small Intestine. PROTEINS -> AMINO ACIDS

* Lipase - Produced in the Pancreas and Small Intestine. LIPIDS -> FATTY ACIDS + GLYCEROL

These diffuse through the lining of the gut into our blood.

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> The stomach produces hydrochloric acid

  - This begins digestion and kills harmful microorganisms.

> Bile is made in the liver and stored in the gall bladder

  - It is released into the small intestine to neutralise the stomach acid, as it is an alkali. It also emulsifies fats to give a bigger surface area.

> The enzymes from the pancreas mix with those made in the small intestine.

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Uses of Enzymes

> Biological Detergents = Protease and Lipase

 - Effective at low temperatures (around 35*C)

 - Digest food stains

> Baby Food = Protease

 - Used to pre-digest proteins during the manufacture of baby foods

> Converting Starch into Sugar Syrup = Carbohydrase

 - Used in foods

> Converting Glucose into Fructose = Isomerase

 - Used in slimming foods as fructose syrup is much sweeter, therefore less is needed

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Aerobic Respiration

- Glucose + Oxygen ---> Carbon Dioxide + Water (+Energy)

- Happens all the time in the cells of animals and plants

- The majority of reactions for aerobic respiration take place in the mitochondria, controlled by enzymes

- Glucose and oxygen go into the cells, and carbon dioxide and water come out

How is the Energy Used?

Living things - Turns Amino Acids into Proteins

Birds and Mammals - Used to contract muscles

Animals - Used to maintain a constant body heat (around 37*C)

Plants - Turns Sugars, Nitrates and other nutrients into Amino Acids

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Exercise and Respiration

- During exercise, muscles require more energy so they can contract

- As the heart rate increases, so does the breathing rate

- The heart pumps blood around the body. It supplies glucose and oxygen to the cells

- Muscles store glucose as glycogen. When exercising, the glycogen is broken down into small glucose molecules

During Exercise

- More glucose and oxygen need to be transported to the muscles, and waste carbon dioxide needs to be romoved quickly.

- To do this, heart rate, breating rate and depth of breathing are increased.

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Anaerobic Respiration

- If you are carrying out very heavy exercise you don't get enough oxygen going to the muscles to carry out aerobic respiration.

- Glucose ---> Lactic Acid (+little energy)

- Lactic acid is toxic so needs to be removed quickly. It causes mucsle fatigue, and they stop contracting efficiently. The blood flows through the muscles to remove the lactic acid.

- Anaerobic respiration involves the incomplete breakdown of glucose

- Oxidation = Process driven by oxygen. Oxygen oxidises the lactic acid.

- Oxygen Debt - After a period of vigourous exercise, we breathe heavily as we are supplying the oxygen needed to break down the lactic acid.

- Once oxygen is provided, the lactic acid can be converted into carbon dioxide and water, which can be removed from the body.

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Mitosis = When body cells reproduce (excluding gametes)

- Mitosis is needed for the growth of cells, and for replacing cells. It can also be used for asexual reproduction.


1) We take a parent cell

2) The genetic material (chromosomes) in the nucleus make identical copies of themselves

3) The chromosomes line up in the centre

4) The copies separate and move apart

5) The cells splits into 2, forming 2 daughter cells

- The process can repeat, each time forming two new cells

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A human body cell contains 23 pairs of chromosomes, in the cell's nucleus.

- Meiosis is a part of sexual reproduction that happens in the reproductive organs. Gametes are made by meiosis

- Fertilisation happens when the male and female gametes join together. Their single 23 chromosomes pair up to gve the full 23 pairs

- The newly formed cell contains a mix of chromosomes from each parent


1) The 23 chromosome pairs start by copying themselves and double up

2) Sections of DNA get swapped between similar chromosome pairs

3) The cell divides into two - with 23 chromosome pairs in each half

4) These two cells divide again and this time the chromosome pairs are split up. The 4 cells we are left with only have 23 single chromosomes in them

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Genetic Variation

- In sexual reproduction, 23 chromosomes are provided from each parent. The newly formed cell contains a mix of cells from each parent, so the mix of DNA is unique.

- Chromosomes are made from DNA. Genes make up DNA.

- Genes control your features.

- Inherited characteristics come from genes.

The sex chromosome pair determines whether you are male or female:

  > Female = x x

  > Male = x y

Alleles can be dominant or recessive. The characteristics controlled by a dominant (D) allele develops if the allele is present on one or both chromosomes in a pair.

The characteristic controlled by a recessive (r) allele develops only if the allele is present in both chromosomes in a pair.

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Mitosis vs Meiosis


- 1 Dvision

- Produces 2 daughter cells, each with 46 chromosomes

- Used for growth, repair, and asexual reproduction


- 2 Divisions

- 1st division: each of the two cells has 46 chromosomes

- 2nd division: each of the four cells has 23 chromosomes

- Used to produce gametes (sperm and egg cells)

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Genetic Disorders

Some disorders are caused by genes and can be inherited.

 > Huntintons Disease - Affects the nervous system. Caused by a dominant allele (DD, Dd).

 > Polydactyly - Born with extra fingers or toes. Caused by a dominant allele (DD, Dd).

 > Cystic Fibrosis - Affects cell membranes, causing certain cells to produce too much mucus (affects breathing and digestion). Caused by a recessive allele (dd)

If a disease is recessive and the person only has one recessive allele (Dd), then that person is a carrier of the disease.

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Stem Cells

Stem cells have the potential to become any other cells in the body. They are unspecialised and undifferentiated.

Empryonic stem cells are found in human embryos. We can also get stem cells from human bone marrow.

Embryonic stem cells are taken from spare embryos from IVF, or may be taken from the umbilical chord of a newborn baby.

Stem cells can be used to treat: Parkinson's disease, spinal chord injuries, and type 1 diabetes. They can also be used to grow new organs.

Social Issues: Save lives, Cure diseases, Save costs.

Ethical Issues: Killing humans? No right to interfere (religious views), violates the Sanctity of Life.

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Structure of DNA

DNA has been supercoiled in order to fit it inside a chromosome. It has a Double Helix Structure.

A gene is a small section of DNA that codes for a protein.

There are four bases of DNA; Adenine, Cytosine, Thymine, Guanine.

Complimentary bases: A-T, T-A, G-C, C-G

Each triplet of bases codes for an Amino Acid. If we know what order to put the amino acids in, we can make a protein.

There are about 20 kinds of Amino Acids.

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Embryo Screening

Embryo screening is a way of checking embroyos to see if they carry the alleles for particular diseases.

How It Works

* Egg cells are taken from the mother and sperm cells are taken from the father and these egg cells are fertillised out side of the body. Once they've been fertilised, you are leftwith an embryo. At the 8 week stage, they can be tested to see if they carry any alleles for a disease. Part of the cell is removed and tested. Once it has been determined/ established, you can implant the embryo back into the mother.

Social Issues: Saves lives, eradicate diseases, improve the quality of life.

Ethical Issues: Killing humans? No right to interfere (religious views), designer babies, chosing gender.

Economical Issues: Save costs, medical treatment, drugs.

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Gregor Mendel - The Father of Genetics

Gregor Mendel was a monk who worked out how characteristics were inherited. He was the first person to suggest the idea of seperately inherited factors.

It took a long time for Mendel's ideas to be accepted by other scientists. This was because they didn't know about chromosomes and genes until after Mendel died. Furthermore, Mendel wasn't a scientist, and his work wasn't published in a science journal.

Mendel decided to breed two different pea plants; a tall one and a short one.

Before Mendel's experiment, it was believed that if you bred a small and tall pea plant, you would produce a medium sized one, however, as Mendel discovered, this was not the case.

Mendel discovered this was not necessarily true, as all of his pea plants were tall.

He then bred these plants (he called them F1) with eachother, however this time, he produced 787 tall plants, and 277 small plants. He simplified this in the ratio 3:1.

Mendel came up with Inheritance Factors - One plant would pass on one factor, and the other would pass on another factor, and, depending on how they combined, you would get certain characteristics and features in the offspring.

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Origins of Life on Earth

It is believed that Earth is about 4500 billion years old, and that life began about 3500 billion years ago.

We can date rocks. Fossils are found in rocks so we can date when different organisms existed.

The Theory of Evolution - The belief that all species on Earth have evolved from simple life forms.

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Fossils are the remains of organisms from many years ago which are found in rocks.

Fossils can be formed from:

 - Hard body parts which don't decay easily (bones, teeth)

 - Parts of organisms which haven't decayed because the conditions for decay are absent, such as in peat bogs or ice. Absent conditions could include there being no oxygen or no microbes.

 - Preserved traces of organisms (footprints)

Most organisms that died didn't leave a fossil as the exact conditions for fossil formation weren't present. Many early life forms had soft bodies so few traces were left behind. Traces which were left behind are likely to have been destroyed by geologicl activity.

Fossils within layers of rocks are reffered to as 'The Fossil Record'

Fossils can show: How new organisms arise, How new species are formed, How some species may become extinct. However, there is uncertainty due to the lack of valid/reliable evidence.

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Extinction can be caused by a number of factors, but always involves a change in circumstances:

 * Climate change - Wooly Mamouth: couldn't adapt to the changes in climate

 * New diseases - Dutch Elm: wiped out by Dutch Elm disease

 * New predators - Dodo: Lived on the island of Mauritious. Rats and humans caused extinction

 * New competitors - Red Squirel vs Grey Squirel

 * A single catastrophic event

Why the dinosaurs became extinct has puzzled many scientists. The two main theories are:

 - The collision of a giant asteroid

 - Sea ice melting and cooling the sea temperature.

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New species can arise as a result of isolation. This is where two populations of a species become geographically separated.

Geographical isolation could occur is an island is separated from mainland or if a new river separates two areas. Mountain ranges and old crators can isolate organisms.

The different organismsm may be exposed to different environmental conditions, food availability or predators.

Natural selection will occur in both areas, but different characteristics will be beneficial in the two populations.

If the populations are brought together and cannot interbreed, we say that they belong to two separate species.

Isolation --> Genetic variation --> Alleles selected --> Interbreeding no longer possible --> New species

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