Cell Activity

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  • Created by: Alishia
  • Created on: 04-05-13 11:35

Cell Structure

Aniaml cells :

  • Nucleus- controls all tha activity of the cell.It conintains the gene on the chromosomes that caryy out instructions for making proteins.
  • Cytoplasm-chemical reactions for life to take place e.g respiration
  • Cell Membrane-passage of substances intio the cell 
  • Mitochondria- in the cytiplasm most of energy is realesed during repsiration
  • Ribosomes- where protein synthesis takes place, making all the proteins needed

Plant and Algal cells:

  • Chloroplast- contian green substance called chlorophyll.Absorbs light energy to make food by photosyntheses.
  • Permanent Vacuole- space in the cytoplasm filled with cell sap.Keeps cell rigid to support the plant.
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Bacteria & Yeast

  • Plamids- small circular bits of DNA
  • Yeast is a single celled organism, anaerobic respiration of yeast sometimes called fermenation
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Specialised Cells

Leaf cell- Absorbs light energy for photosynthesis Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.

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

Sperm cell- Fertilises an egg cell - female gamete-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.

Red blood cells- Contains haemoglobin to carry oxygen to the cells.-Thin outer membrane to let oxygen diffuse through easily. Shape increases the surface area to allow more oxygen to be absorbed efficiently. No nucleus, so the whole cell is full of haemoglobin.

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Diffusion is the net movement of particles from an area where they are at a HIGH concentration to an area where they are at a LOWER concentration , DOWN a concentration gradient.

  • The greater the difference in concentration the faster the rate of diffusion 
  • Dissolved substances such as glucose and gases such as oxygen move in and out of cells by diffusion 
  • Oxygen required for respiration passes through cell membranes by diffusion

net movement= particles moving in - particles moving out

Cell Membrane:

  • Increasing the surface area means more room for diffusion to take place
  • Folding up the membrane of a cell, pr tissue lining an organ area which diffusion can take place is increased 
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Osmosis is a special case of diffusion.it is the movement of water from dilute to a more concentrated solution through a partially permeable membrane that allows water to pass through.

Differences in the concentrations of solutions inside and outside a cell cause water to move into or out of the cell by osmosis.

  • Isotonic-concentration of solutes in the solution outside the cell is THE SAME as the concentration inside the cell.
  • Hypertonic-concentration of solutes in the solution outside the cell is HIGHER than the concentration inside the cell 
  • Hypotonic-concentration of solutes in the solution outside the cell is LOWER than the concentration inside the cell

Plants: Osmosis is important to maintain turgor in plant cells.of more water is lost by osmosis, the vacuole and cytoplasm shrink, and eventually the cell membrane pulls away from the cell wall -plasmolysis

Animal cells can be damaged if the concentrations inside and outside the cells are not kept the same.

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Active Transport & Exchanging Materials

Substances are sometimes absorbed UP a concentration gradient by active transport

  • Active transaport uses energy from respiration , Cells an absorb ions from very dilute solutions,and actively absorbs substances such as sugar and salt against a concentration gradient, using active transport
  • Useful for plants to obtain nitrate ions found in very dilute solutions, Similarly sugar , such as glucose, is always actively absorbed out of your gut and kidney tubules into your blood.

Single - celled organisms have a relatively large surface areas to  volume ratio so all necessary exchanges with the environment take place over this surface,

In multicelluar organismas many organs are specialsed with effective exchange surfaces.

Exchange surface usually have a large surface area and thin walls, which give short diffusion distances.In animals. exchange surfaces will have an efficent blood supply or, for gaseous exchange, be ventilated.

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Exchange in the gut

  • The villi in the small intestine provide a large surface area with an extensive network of blood capillaries
  • The villi mean the small intestine is well adapted as an exchange surface to absorb the products of digestion, both by diffusion and by active transport.
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Cell Division

  • new cells are nbeeded for an organism
  • new cells must have the same gentic information as the orginals so they can do the sam job
  • Nucleus contains chromosomes

Chromosomes :  cary the gene that contains the instructions for making both new cellas and all the tissue and organs needed to make entire new you.

Gene-samll packet of information that contorls a charatristic ~(section of DNA)

Allels-different forms of a gene, for example gene which determines wethere or not yo have dimples.

You have 46 chromosomes in the nucleus of your body cells, arranged into 23 pairs, one of each pair is inherited from your father and one from your mother.Your sex cells (gamets) have only one of each pair of chromosomes.

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  • Cell Division in normal body dells produses two IDENTICAL cells
  • produces additional cells needed for growth or replacement
  • Asexual Repoduction - the cells of teh offspring are producesd by mitosis from the cells of their parents.Conatin exactly the SAME allelsas theri parents

When a body cell divides by mitosis:

  • copies of the genetic material are made
  • the cell then divides once to form two genetically identical body cells.

cell divides in two ----> forms two daughter cells ---->duaghter cells contains 4 chromosomes indentical to the ones in the orginal parent cell.

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Animals and Humans

  • early development of animals and plant embroys, the cells are unspecialised- known as a stem cell.
  • In a mature (adukt) anmial, cell division is mainly restricted.
  • Specilaied cells can divide by mitosis 
  • Goriwth stops once teh animals is matured
  • blood and skin cells CANNOT divideso ADULT STEM CELLS replace dead or damaged cells


  • Plant cells are able to differentiate all through their lives
  • can redifferentaire to another plant cell and become a complte;y different type of cell.
  • Cloning- identical offspring
  • produced by a tuny piece if leaf tissue
  • right condiotions can undergo mitosis many times
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  • Meiosis results in sex cells, called gametes, with only half the original number of chromosomes
  • Female gametes or OVA made in the ovaries
  • Chromosomes reduced by half in the following way:
    • When a cell divide to form gametes, the chromosomes are copied so there are four sets of chromosomes instead of the normal two sets.Similar to mitosis
    • The cell then divides twice in quick session to form four gametes, each with a single set of chromosomes 
  • Each gamete is slightly different ,contain random mixtures of the original chromosome pairs.
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Fertilisation and Variation


  • Each sex cell has a single set of chromosomes
  • when 2 sex cells join during fertilisation , the single new cell formed has a full set of chromosomes
  • humans, the gg cell (ovum has 23 chromosomes as well as the sperm cell.
  • Produce a single new body with 46 chromosomes
  • Once fertilisation is complete , the unique new cell begins to divide by mitosis to form new individual.


  • Asexual Reproduction- offspring produced as a result of mitosis from the parent cell.Exactly the same chromosomes and the same genes as their parent 
  • Sexual Reproduction - gametes produced by meiosis in the sex organs of the parents, introduces variety as each gamete is different.
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Stem Cells

  • An egg and sperm cell fuse together to form a Zygote
  • that cell dividesannd becomes a hollow ball of cells - the Embryo
  • The inner cells of this balls are the Stem Cells

Cells from human embryos and adult bone marrow, called stem cells, can be made to differentiate into many different types of human cell, eg nerve cells.

Embryonic Stem Cells and Stem cella can be made to differentiate into many different types of cell

Stem cells have the potential to treat previosly incurable conditions.We may be able to grow nerve cells to cure paralysis or whole new organs for people who need them.

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Cell Growth and Cancer

Tumors result from the abnormal, uncontrolled growth of cells.

Benign tumours form in one place and do not spread to other tissues

Malignant tumours (cancer)  invade healthy tissues and may spread to other healthy tissues in the bloodstream to form secondary tumours

Tumours can be caused by a number of factors, including chemical carcinogens(tar found in tobacco) and ionising radiation (uv light and x-rays)

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