Topic 1 Biology GCSE New specification

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  • Created by: millieray
  • Created on: 14-12-17 16:59

Prokaryotic and Eukaryotic

  • All living things are made of cells.
  • Cells can be either prokaryotic or eukaryotic.
  • Eukaryotic cells are complex and include all animal and plant cells.
  • Prokaryotic cells are smaller and simpler, e.g. bacteria.
  • Eukaryotes are organisms made up of eukaryotic cells.
  • A prokaryote is a prokaryotic cell (it's a single celled organism)
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Animal Cells

  • The different parts of a cell are called subcellular structures.
  • Nucleus - contains genetic material that controls the activities of the cell.
  • Cytoplasm - gel-like substance where most of the chemical reactions take place. It contains enzymes that control these chemical reactions.
  • Cell membrane - holds the cell together and control what goes in and out.
  • Mitochondria - these are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.
  • Ribosomes- these are where protiens are made in te cell.
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Labelled diagram of animal cell and plant cell

Image result for labelled animal and plant cells gcse

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Plant cell

  • Plants have all the features of an animal cell with these added ones:
    • Rigid cel wall- made of cellulose. It supports the cell and strengthens it.
    • Permanent vacuole- contains cell sap, a weak solution of sugar and salts.
    • Chloroplasts- these are where photosynthesis occurs, which akes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.
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Bacterial cell

  • Bacteria are prokaryotes. The features of a bacterial cell are:
    • Cell membrane
    • Cell wall
    • Cytoplasm
    • Plasmids- these are small rings of DNA
    • They don't have a nucleus - instead they have a single circular strand of DNA that floats freely in the cytoplasm
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Labelled bacterial cell

Image result for bacterial cell labelled gcse (http://www.docbrown.info/page20/page20images/BacteriaCell1.gif)

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microscopy

  • Light microscopes use light and lense to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures, like nuclei.
  • Electron microscopes use electrons instead of light to form an image. They have a much highrt magnification than light microscopes.
  • They also have a higher resolution. (resolution is the ability tp distinguish between two points, so a higher resolution gives a sharper image)
  • Electron microscopes let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts.
  • You can calculate magnification using: Magnification= Image size                                                                                   Real size
  • Example: A specimen is 50μm wide. Calulate the width of the image of the specimen under a magnification of x 100. Give your answer in mm.
    • Image size= magnification x real size
    • Image size= 100 x 50
    • Image size= 5000μm
    • Image size= 5mm
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cell differentiation

  • Differentiation is the process by which a cell changes to become specialised for its job.
  • As cells change, they develop different subcellular structures and turn into different types of cells. This allows them to carry out specific functions.
  • Most differentiation occurs as an organism develops. In most animal cells, the ability to differentiate is lost at an early stage, after they become specialised. However, lots of plant cells don't ever lose this ability.
  • The cells that differentiate in mature animal cells are often used for repair and replacing cells.
  • Some cells are undifferentiated cells- these are called stem cells.
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Specialised Cells In Animals

  • Sperm Cell
    • These are specialised for reproduction. Their function is to get the male DNA to the female DNA.
    • it has a long tail and a streamlined head to help it swim to the egg.
    • there are lots of mitochondria in the cell to provide the energy needed.
    • It also carries enzymes in its head to digest through the egg cell membrane.
  • Nerve Cell
    • Its function is to carry electrical signals from one part of the body to another.
    • It is specialised for rapid signalling.
    • They are long to cover more distance and have branched connections at their ends to connect to other nerve cels and form a network throughout the body.
  • Muscle Cells
    • Their function is to contract quickly and are specialised for contraction.
    • They are long to have more space to contract and contain lots of mitochondria to generate the energy needed for contraction.
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Specialised cells in plants

  • Root hair cells
    • These are cells on the surface of plant roots which grow into long hairs and stick out into the soil, that are specialised for absorbing water and minerals.
    • This gives the plant a big surface area for absorbing water and mineral ions from the soil.
  • Phloem and Xylem cells
    • These form phloem and xylem tubes, which transport substances such as food and water around plants. They are specialised for transporting substances.
    • The cells are long and joined end to end to form the tubes.
    • Xylem cells are hollow in the centre and phloem cels have very few subcellular structures, so that stuff can through them.
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Chromosomes

  • Most cells in your body have a nucleus. The nucleus contains youir genetic material in the form of chromosomes.
  • Chromosomes are coiled up lengths of DNA molecules.
  • Each chromosome carries a large number of gene. Different genes control the development of different characteristics e.g. hair colour.
  • Body cells normally have two copies of each chromosome-one from the organism's 'mother', and one from its 'father'. So, humans have two copies of chromosome 1, two copies of chromosome 2, etc.
  • There are 23 pairs of chromosomes in a human cell.
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Cell cycle

  • Body cells in multicellular organisms divide to produce new cells as part of a sereies of stages called the cell cycle.
  • The stage of the cell cycle when the cell divides is called mitosis.
  • Multicellular organisms use mitosis to grow or replace cells that have been damaged.
  • The end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes.
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The stages of the cell cycle

  • The two main stages of the cell cycle are:
    • Growth and Repair: In a cell that's not dividing, the DNA is all spread out in long strings.
    • Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes.
    • It then duplicates its DNA- so there's one copy for each new cell. The DNA is copied and forms X-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of each other.
    • Mitosis: Once its contents has been copied the cell is ready for mitosis. The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
    • Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells- the nucleus has divided.
    • Lastly, the cytoplasm and cell membrane divide. The cell has produced two new daughter cells. The daughter cells contain exactly the same DNA- they're identical. Their DNA is also identical to the parent cell.
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Mitosis

Image result for mitosis

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Binary Fission

  • Prokaryotic cells replicate by binary fission.
  • In binary fission the cell splits in two.
    • The circualr DNA and plasmid(s) replicate.
    • The cell gets bigger and the circular DNA strands move to opposite 'poles' of the cell.
    • The cytoplasm begins to divide and new cell walls begin to form.
    • The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have variable numbers of copies of the plasmid(s)
  • Bacteria can replicate very quickly if given the right conditions.
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Diagram of Binary Fission

Image result for binary fission gcse biology (http://academic.pgcc.edu/~kroberts/Lecture/Chapter%2011/11-02_BinaryFission_0_L.jpg)

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Stem Cells

  • Undifferentiated cells called stem cells, can divide to produce more undifferentiated cells. They can differentiate into different types of cell, depending on instruction.
  • Stem cells are found in early human embryo. These stem cels have the potential to turn into any kind of cell.
  • Adults also have stem cells but these are only found in certain places (like bone marrow) and can't turn into any cell, only certain ones such as blood cells.
  • Stem cells from embryos and bone marrow can be cloned in the lab to produce genetically identical cells and made to differentiate into specialised cells to use in medicine or research.
  • Medicine already uses adult stem cells to cure diseases. For example, stem cells from a healthy person's bone marrow can replace faulty blood cells in another patient.
  • Embryonic-stem cells could also be used to replace faulty cells- you could make insulin-producing cells for people with diabetes or nerve cells for paralysed people.
  • In a type of cloning, called therapuetic cloning, an embryo could be made to have the same genetic information as the patient, meaning the stem cells produced would have the smae genes and wouldnt be rejected by the patient.
  • There are risks- for example, a stem cell made in a lab could be contaminated with a virus which could then be passed on to the patient.
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For and Against Stem Cell Research

  • some people feel human embryos shouldn't be used since each one is a potential human life.
  • others believe curing existing patients who are suffering is more important than an embryos rights. A convincing argument for this is that the embryos used in research are usually unwanted ones from fertility clinics which would have been destroyed if not for the research.
  • Campaigners feel that scientists should work on developing new and other sources of stem cells, so people can be helped without using embryos.
  • In some countries stem cell research is banned, in the UK there are strict guidelines to follow.
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Producing Identical Plants

  • In plants, stem cells are found in the meristem.
  • Throughout the plant's entire life, cells in the meristem tissues can differentiate into any type of plant cell.
  • These stem cells can be used to produce clones of the whole plant quickly and cheaply.
  • They can be used to grow more rare plant species preventing extinction.
  • Stem cells can also be used to grow crops identical to plants with desired features for farmers- e.g. disease resistance.
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exhange surfaces

  • Organisms exchange substances with their environment.
  • Cells can use diffusion to take in substances they need and get rid of waste products. For example:
    • oxygen and carbon dioxide are transferred between cells and the environment during gas exchange.
  • How easy it is for an organism to exchange substances with its environment depends on the organism's surface area: volume ratio (SA:V)
  • A ratio shows how big one value is compared to another. The larger the organism is, the smaller its surface area is compared to its volume. You can show this by calculating surface area to volume ratios.
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Multicellular organism exchange surfaces

  • In single celled organisms, gases and dissolved substances can diffuse directly into the cell across the cell membrane. It's because they have a large surface area to volume ratio, so enough substance can be exchanged across the membrane to supply the cell.
  • Multicellular organisms have a smaller surface area to their volume, so not enough substance can diffuse from their outside surface to supply their volume. This means they need an exchange surface for efficient diffusion.
  • Exchange surfaces are adapted to maximise effectiveness:
    • They have a thin membrane, so they have a short diffusion distance.
    • They have a large surface area creating a large area for diffusion.
    • Exchange surfaces in animals have lots of blood vessels to increase diffusion speed.
    • Gas exchange surfaces in animals are often ventilated so air moves in and out.
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Examples of exchange surface in humans

  • Gas Exchange in the Lungs
  • The lungs contain millions of little air sacs called aveoli where gas exchange takes place. 
  • The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. They have:
    • A large surface area
    • A moist lining for disolving gases
    • Very thin walls
    • A good supply of blood.
  • Villi in the small intestine:
  • The inside of the small intestine is covered in millions of tiny projections called villi.
  • They increase the surface area in a big way so that digested food is absorbed quickly into the blood. They have:
    • a single layer of surface cells
    • a very good blood supply to assist in quick absorption
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Comments

malindavue

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Some useful revision cards on photosynthesis that could be used to test your knowledge of the key facts in this wordle unlimited topic that is found in nearly all science specifications. I've added a sample examination question at the end which is a good way to test whether you have grasped the key concepts as well as testing yourself using the revision cards.

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