Cell structure & organisation

Cell Structure and Organisation

T H E M E O N E : P R I N C I P L E S O F B I O L O G Y

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• Identify the main organelles and membranes in the cell.

• Explain the various functions of the different organelles.

• Compare the structure of plant and animal cells.• Describe the relationship between structure and

function as seen in root hair cells, xylem vessels and red blood cells.

• Differentiate between the levels of organisation in an organism.

Learning Outcomes



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• A light microscope uses light rays to produce images; an electron microscope uses electron beams.

• Magnification: degree to which the image is enlarged.

1.1 Structure of Cells



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• Resolution: the smallest distance needed for two points to be distinguished.


• Depth of field: different tissues lie on different planes.



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• Preparing slides for use with the light microscope:




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• Caring for the microscope:– When shifting the microscope, hold on to the

microscope handle with one hand and support the base with the other. Do not swing it around.

– Do not touch the lenses with your fingers and use only lens paper to clean the glass.

– Before keeping the microscope, first rotate the nosepiece to the low power objective, then lower it until it nearly touches the stage.

– Be careful when working with the slides and cover slips.




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• Prokaryotes do not have a nucleus and are more primitive.

• Eukaryotes like the animal cell (left) and plant cell (right) have a nucleus where the genetic material resides.




C h a p t e r 11.1 Structure of Cells



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Nucleus• Chromosomes are uncoiled chromatin, visible

during nuclear division.• A man has 46 chromosomes (i.e. 23 pairs of

chromosomes) in all his cells except the sex cells.




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Nucleus

• Nucleolus is the most visible part, responsible for formation of ribosomes.




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Endoplasmic Recticulum (ER)• Extension of the outer layer of nuclear membrane.




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Endoplasmic Recticulum (ER)

• Smooth ER:– Without ribosomes– Responsible for producing lipids and cholesterol.– Where harmful substances are detoxified.

• Rough ER:– With ribosomes.– Where proteins are synthesised.




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Golgi Body

• Stack of membrane-enclosed sacs.• Modify small vesicles from ER:

– Small vesicles fuse with one side of this complex.– Finished products bud off from the opposite face.




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Mitochondria

• Double-membraned organelle.• Cristae is the inner membrane, thrown into deep

folds.




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Mitochondria

• Energy extracted from sugar molecules is stored in bonds of adenosine tri-phosphate (ATP) molecules.

• Bonds can be easily released with the help of enzymes during respiration.




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Vacuole• Fluid-filled sacs.




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• Vacuoles in animal cells are called vesicles; they are temporary and have different functions such as:

– Storing sugars.– Transporting products.– Containing digestive enzymes

to digest invading bacteria.– Helping the cell expel excess

water.

1.1 Structure of CellsVacuole



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• Plant cells have a large and relatively permanent central vacuole.

1.1 Structure of CellsVacuole



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Cytoplasm and Plasma Membrane1.1 Structure of Cells

• The fluid in which all organelles are suspended is known as the cytosol (in blue).

• The plasma membrane (in orange) controls substances entering or leaving the cell.



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Cytoplasm • Entire region of the cell between the nucleus

and the plasma membrane.• Includes the organelles, various membrane and

cytosol.




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Plasma Membrane• Transfers chemical messages from the outside of the

cell to the inside.• Keeps the cell contents in place.• Made of lipids and proteins.• Constantly reforms to allow movement of materials

into and out of the cell.




C h a p t e r 11.1 Structure of Cells



C h a p t e r 11.1 Structure of CellsCell Wall• Only in plant cells.• Presence of strong cellulose

fibrils for reinforcement.• Functions:

– Protects the cell from harmful external influences

– Helps the cell keep its shape– Prevents the cell from

absorbing too much water that it bursts.



C h a p t e r 11.1 Structure of CellsCell Wall

• Plasmodesmata are channels that allow small molecules and water molecules to move between plant cells.



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Central Vacuole

• Makes up 90% of the cell’s volume in a fully grown plant.




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Central Vacuole• Tonoplast is the membrane enclosing the cell sap

which is mainly water.• Maintains turgidity of the cell.• Stores nutrients, wastes, pigments and poisonous

substances.




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Chloroplasts

• Oval or spherical.• Found only in plant cells.




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Chloroplasts• Give plant cells their green colour.• Give petals and fruits their colour.• Others do not contain colour but act as centres of

starch grain storage or storage of oils and proteins.




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• The cell is the basic unit of all living organisms.• All activities of the cell are controlled by

information stored in the nucleus.• Mitochondria in the cell extract energy from

glucose and store it as ATP molecules.• The energy stored in ATP is used by various

organelles in the cell such as the ribosomes, which use the ATP to produce proteins for cell repair or for export to other parts of the organisms.



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• The plasma membrane controls the movement of substances into or out of the cell.

• Plant cells are rigid because of the cell wall surrounding the cell. The cell wall helps to provide support for the plant.

• Unlike the temporary small vacuoles of animal cells, plant cells usually have a permanent, large, central vacuole. This helps to maintain the shape of the cell as well as store various substances.

• The most characteristic feature of the plant cell is the chloroplast which allows the plant to make food in the presence of sunlight.



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Xylem Vessels• Pipe-like columns.• Provide support.• Transport water

and mineral salts from roots to other parts.

1.2 Specialised Cells, Tissues and Organs



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Root Hair Cell• Long narrow extension of the cell.• Increases cell surface area.• Increases the rate of diffusion of water and mineral

salts.




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Red Blood Cell

• Contains red pigment called haemoglobin.• Supplies oxygen to other body cells.




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Relationship Between Structure and Function of Red Blood Cell


• Haemoglobin combines easily with oxygen.• Absence of nucleus – can pack more haemoglobin.• Biconcave shape – increases surface area.• Thin and elastic plasma membrane – able to squeeze

through narrow capillaries.



C h a p t e r 11.2 Specialised Cells, Tissues and OrgansCell, Tissue, Organ and Organ System• Similar cells work together as a tissue

to carry out a particular function.• Organs contain a number of different

kinds of tissues.• Several organs may work together in

an organ system.• Each organ system serves a specific

function.



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• The structure of a cell is related to its function.• Similar cells work together as a tissue to carry

out a particular function.• Organs contain a number of different kinds of

tissue.(a) (b) (c) (d)



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• Several organs may work together in an organ system.

• Each organ system serves a specific function. Most activities involve more than one organ system functioning at the same time.



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Cell structure & organisation

Science

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