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Using a microscope | Cell structures | Cell types | Tissues | Organs
Cells are small!
A microscope is needed to see cells.
Cells need to be small in order to work efficiently.
The cell is to biology as the atom is to chemistry – cells are the elementary structural unit of all living organisms.
New cells are formed by the division of living cells.
Cell division produces new cells for growth, repair and reproduction.
We each began life as one cell and now we are make up of 100,000,000,000,000 cells and each second of our life we make 50,000,000 new cells.
Using the microscope to view cells
- Switch on light or adjust the mirror to get good light.
- Place a small piece of onion epidermis on the glass slide.
- Place a drop of water on the plant tissue.
- Lower the cover slip gently onto the slide to cover the plant tissue.
- Place the slide on the stage of microscope.
- Turn the lowest power objective lens (X4) until it is ‘clicked’ into position.
- Turn the coarse focussing wheel to bring the lens as close to the slide as possible.
- Look through eyepiece and turn coarse focusing knob to slowly move lens away from slide until plant tissue is in focus.
- Observe the plant cells and move the slide to scan the tissue.
- Before increasing the magnification, move the area of greatest interest into the very centre of your field of view.
- Click the next higher objective lens (X10) into position.
- Only turn the fine focusing wheel to sharpen the image.
- Note the greater detail – draw a labelled diagram of part of the tissue.
- Before increasing the magnification, move the area of greatest interest into the very centre of your field of view.
- Click the highest objective lens (X40) into position.
- Only turn the fine focusing wheel to sharpen the image.
- Note the greater detail – draw a labelled diagram of a plant cell.
When finished: click the lowest power objective into position and turn the coarse focusing wheel to move the objective as far away as possible from the stage.
Iodine may be used to stain plant cells for microscopic examination.
Methylene blue is used to stain animal cells e.g. human cheek cells.
Cell structures
Structures common to plant and animal cells
Nucleus: has DNA, the genetic material; controls cell structure activity.
Chromosomes: made of DNA and protein, found in nucleus.
Gene: a particular section of DNA, which controls a definite inherited trait.
Cell membrane: surrounds the cell keeping all its contents close together; controls movement of substances in and out of cell keeping its chemistry perfect.
Cytoplasm: a complex sticky solution where many chemical reactions take place.
Structures in plant cells but not in animal cells
Cell wall: made of cellulose, strengthens and supports cell; prevents the cell bursting.
Chloroplast: photosynthesis, present in green plant cells; contains green plant pigment chlorophyll, which absorbs the light energy needed for photosynthesis.
Vacuole: stores water, food, minerals and waste; plays a support role in the soft non-woody parts of plants; the liquid of the vacuole is called cell sap.
Note: plant cells are generally much bigger than animal cells; plant cells store excess glucose as starch.
Cell types
Plants and animals contain many different types of cells, which are adapted for their function – the human body has about 300 different types of cells.
Muscle cells: contract to cause movement – move bones, move food along the gut, move blood along the blood vessels.
Nerve cells: their long fibres carry messages directly and quickly to their target.
Red blood corpuscles: contain haemoglobin to transport oxygen efficiently.
White blood cell: give protection against disease causing organisms and cancer.
Leaf cells: contain chloroplasts for photosynthesis.
Root hair cells: have large surface area to take up water and minerals from soil.
Parenchyma cells: store starch.
Epidermal cells: protect the surface of leaves.
Tissues
A tissue is a group of similar cells specialised to carry out a particular job.
Muscle cells: form muscle tissue for movement.
Nerve cells: form nerve tissue for rapid transfer of information.
Bone: plays an important role in protection, support and movement in the body.
Blood: transports materials throughout the body – can be considered to be a complex tissue as it has a number of different cell types.
Xylem tissue transports water in a plant.
Phloem tissue transports food in a plant.
Photosynthetic tissue in a leaf produces food for the plant.
Parenchyma is storage tissue and holds food in reserve for later use.
Organs
An organ is a group of tissues working together to carry out a particular job.
Heart: a mixture of muscle and nervous tissue – its job is to pump the blood.
Lungs: their job is to absorb oxygen and excrete carbon dioxide.
Stomach: its job is to digest protein plus absorb water, glucose and minerals.
Brain: its job is to control the body’s activities, think, learn and make decisions.
Root: anchorage, food storage, water and mineral absorption are its main jobs.
Stem: support the leaves, buds and flowers; food storage,
Leaf: photosynthesis and transpiration.
Flower: sexual reproduction – pollination, seed formation and seed dispersal.
Organs cannot work by themselves; they depend on other organs to supply things they need.
Systems
A system is a group of organs working together to carry out a particular job.
Digestive: oesophagus, stomach, liver, pancreas, small intestine, large intestine.
Nervous: brain, spinal cord, nerves, eyes, ears, taste buds, nose, skin, nerves.
Circulatory: heart, arteries, veins, blood.
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