2.1 CELL STRUCTURE. The cell is the smallest unit of living organisms that shows the characteristics of life.

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Gervase Walters
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1 2.1.1 Microscopy The cell is the smallest unit of living organisms that shows the characteristics of life. A general introduction to the microscope. The light microscope All cells are microscopic which means they can only be seen with the help of a microscope. The light microscope is the most commonly used microscope in biology. It uses light to show the image. Light microscopes are also known as compound microscopes because they use two lenses an eyepiece lens and an objective lens. The best light microscope will only magnify an image about 1000 times. The total magnification of a microscope is calculated by multiplying the magnifying power of the eyepiece lens by the magnifying power of the objective lens. s of the parts of the light microscope Part Eyepiece Nosepiece Objective lens Stage Stage Clips Diaphragm Coarse focus wheel Fine focus wheel Light source (mirror) Magnifies the image Rotates in order that an objective lens can be used Magnifies the image Holds the microscope slide Holds the microscope slide in place Controls the amount of light passing up through the slide Used to make large adjustments in image clarity Used for make smalls adjustments in image clarity Shines light up through the slide

2 The Transmission Electron Microscope (TEM) The transmission electron microscope (TEM) is a very powerful microscope. This microscope sends a beam of electrons through the specimen. This shows the internal structure of the specimen in great detail. The image is produced on a screen or photograph. So the transmission electron microscope gives higher magnifications, greater resolution and greater detail than the light microscope Cell Structure and Components of the cell under the light microscope and their functions. Animal cells: cytoplasm and nucleus. Plant cells: cell wall, cytoplasm, nucleus, vacuole, and chloroplast.

3 Cell Component Cytoplasm Nucleus Cell membrane Cell wall Vacuole Chloroplast Site of chemical reactions Controls the cell s activities Semi-permeable, controls what enters and leaves the cell Gives the cell strength and support Stores sugars & salts, gives the cell turgor (rigidity) Carry out photosynthesis Position and function of cell membrane The cell membrane surrounds both plant and animal cells. Its function is to allow only certain things in or out of the cell i.e. it is semi-permeable (selectively permeable) Cell Ultrastructure

and of the Cell Membrane Cell membranes surround cells and all membranes have the same structure.

There are proteins embedded in the phospholipid bilayer.

4 and of the Cell Membrane Cell membranes surround cells and all membranes have the same structure. They are made of a double layer of phospholipids. There are proteins embedded in the phospholipid bilayer. This concept of cell membrane structure is called the Fluid Mosaic Model To control what enters and leaves the cell semi-permeable. To hold the cell contents To recognise foreign particles and sense molecules that touch them and of the Mitochondrion Mitochondria have a smooth outer membrane and a folded inner membrane with many infoldings called cristae. They also have their own DNA.

To supply energy to the cell. They carry out respiration powerhouse of the cell.

Inactive cells have few mitochondria fat in humans and ground tissue in plants and of the Chloroplast Chloroplasts are only found in

They have a double membrane on the outside and inside there are stacks of membranes called grana which are found in the liquid called

5 To supply energy to the cell. They carry out respiration powerhouse of the cell. Active cells have a lot of mitochondria muscle, brain and liver cells in humans, meristematic cells (shoot and root tips) in plants. Inactive cells have few mitochondria fat in humans and ground tissue in plants and of the Chloroplast Chloroplasts are only found in plant cells. They have a double membrane on the outside and inside there are stacks of membranes called grana which are found in the liquid called stroma. The green pigment (colour) chlorophyll is contained in the grana. To carry out photosynthesis (Use light to make food for the plant). and of the Nucleus The nucleus is surrounded by a double membrane which contains many nuclear pores. It contains a nucleolus which makes ribosomes and heredity material called chromatin.

To control the cells activities. It is the control centre of the cell. and of Nuclear Pores Nuclear pores are small holes found in the nuclear envelop or double membrane.

Genes are found on the chromosomes and are sections of DNA that contain the code for making proteins. The chromosomes are usually in the form of fine threads called chromatin.

6 To control the cells activities. It is the control centre of the cell. and of Nuclear Pores Nuclear pores are small holes found in the nuclear envelop or double membrane. To allow chemicals to pass in and out of the nucleus. and of DNA DNA (Deoxyribonucleic acid) is found in the nucleus in structures called chromosomes. Genes are found on the chromosomes and are sections of DNA that contain the code for making proteins. The chromosomes are usually in the form of fine threads called chromatin. To regulate the making of proteins in the cell and of Ribosomes Ribosomes are tiny organelles found in the cytoplasm of the cell. They are made of RNA and protein and consist of two pieces or subunits ( like a burger bun!) To make proteins. They do this by joining amino acids.

7 H Prokaryotic and Eukaryotic Cells Cells are divided into two main types: 1. Prokaryotic cells Prokaryotic cells have no true nucleus. They have a loop of DNA which is found in the cytoplasm. They have no mitochondria or chloroplasts. They are small primitive cells. Bacteria cells are the only prokaryotic cells that exist. Prokaryotic cells do not have a membrane- bound (true) nucleus or membrane-bound organelles like mitochondria and chloroplasts. 2. Eukaryotic cells Eukaryotic cells have a true nucleus. Their DNA is enclosed by a nuclear membrane. They have mitochondria and chloroplasts. They are larger and more advanced cells and evolved from prokaryotic cells. Most organisms (plants, animals and fungi) are eukaryotes Eukaryotic cells have a membrane-bound (true) nucleus and membrane-bound organelles like mitochondria and chloroplasts.

Chapter 7 Cell Structure

Chapter 7 Cell Structure Mr. C. Biology 1 07 Cell Structure Chapter 7 Cell Structure All living things are made of cells. Cells are made up of 3 main parts, Cell Membrane A skin that controls what enters