wonderful world of cells
TRANSCRIPT
The wonderful world of cells!
A fascinating insight into the world of cells, who discovered them, the different types and what they are made up of.
Microscopes Light microscope Electron microscope
Uses light rays Uses electron ‘beams’
Magnification – x2000 Magnification – x500,000
Resolving power – 200nm Resolving power – 1nm
Focused by glass lenses Focused by electromagnets
Specimens can be living or dead
Specimens must be dead
Small, portable and relatively inexpensive
Large, static and very expensive
Microscopes Magnification – to make an image appear bigger To calculate the magnifying power of a
microscope:
eye piece lens magnification X objective lens
Resolution – the minimum distance between 2 points at which they are still visible as 2 separate points
Robert HookeHe looked at cork cells under a microscope and used the term ‘cell’. The holes that he observed where once filled with living material (cytoplasm)
Robert Hooke’s cells
Theodor Schwann
Matthias Schleiden
Cell theorySchwann and Schleiden came up with the cell
theory.
They proposed that all plants and animals were made up of cells and that cells were the basic units of life
Another scientist, Rudolf Virchow discovered that new cells can only arise from the division of pre-existing ones.
Prokaryotic and Eukaryotic cells No true nucleus Few organelles except for
small ribosomes Single strand of genetic
material free in the cell Simple structure Small in size Include bacteria and
blue/green algae
Distinct nucleus surrounded by a nuclear envelope
Many membrane bound organelles
Genetic material is stored in the nucleus
Highly organized to carry out complex functions
Large in size Include plants, animals
and fungi
Eukaryotic cell
Animal cells: these are cheek cells as seen with a compound microscope, compare these cells to the next ones seen through an electron microscope.
Plant and animal cells Cellulose cell wall Chloroplasts Large permanent
vacuole with cell sap No centrioles Starch grains for
storage
No cell wall No chloroplasts Small, temporary
vacuoles Centrioles present Glycogen granules
for storage
Plant cell
Animal cell
Cytoplasm
Watery, jelly-like material
Contains many substances for metabolism
The other organelles are suspended in it
Cellulose cell wall
Many cellulose fibers glued together Strong to resist expansion of the cell as
water enters – this supports the cell Provides mechanical strength to the cell Freely permeable
Vacuole Large permanent vacuole in plant cells is
called a central vacuole. It contains cell sap, a solution of sugar and minerals.
They are food stores They accumulate waste products Some contain pigments to give color Vacuoles in animal cells are small and
temporary
Nucleus Largest cell organelle Surrounded by a double membrane that
allows materials to pass in and out Contains genetic material (DNA) which is
used to make proteins Controls the metabolic activity of the cell
Nucleolus Found in the nucleus Dense, spherical structure Contains RNA for the production of
ribosomes
Ribosomes
Small, dense organelles Can be free in the cytoplasm or attached to
rough endoplasmic reticulum They are made in the nucleolus They are the site of protein synthesis
Endoplasmic reticulum Complex system of double membranes with
fluid-filled sacs in between called cisternae Connected with the nuclear membrane and the
cell membrane It collects, stores and distributes materials Rough endoplasmic reticulum has ribosomes on
it. It packages and transports proteins made by ribosomes
Smooth endoplasmic reticulum is the site of lipid (fat) synthesis.
Golgi complex Also known as golgi body or apparatus Made from small pieces of rough ER
pinched off at the end to form vesicles which fuse together
Site of protein modification Vesicles pinch off at the ends to carry the
new chemicals away (some vesicles become lysosomes)
Lysosomes Small vesicles formed when pieces of the golgi
body pinch off Contain hydrolytic enzymes that can digest cell
material They destroy worn out organelles They can destroy material brought into the cell
(e.g. bacteria) They can release enzymes out of the cell to digest
other cells They can cause the cell to self destruct
Mitochondria Has a double membrane. The outer one
controls entry of materials and the inner one has many folds called cristae
Has a matrix containing DNA, ribosomes and enzymes
Site of aerobic respiration The more active the cell, the more
mitochondria it has
Chloroplasts
Found in plants cells that carry out photosynthesis They are the site of photosynthesis They have a double membrane filled with fluid
(stroma) where the photosynthesis reactions take place
The stroma contains piles of flattened scas (grana) where chlorophyll is found and light is absorbed
Cytoskeleton This is a network of fibrous proteins It allows movement and gives the cell
shape and support It is made up of microtubules and
microfilaments
Centrioles These are 2 short bundles of microtubules
positioned at right angles to each other. They are found just outside the nucleus in
animal cells During cell division, they move to opposite
ends of the cell and produce the spindle
Flagella
Also made up of microtubules
Often used to help cells move (e.g. sperm)
Cell membrane
Made up of a bilayer of phospholipids that allows some materials through but not others (semi-permeable)
Contains proteins that can act as pores, carriers or be involved in cell recognition
The main function is to regulate the movement of molecules and ions
Cell membrane structure Made up of a bilayer of phospholipids.
They have a polar end (water liking) and a non-polar end (water hating)
Protein carrier molecules are found embedded in the cell membrane; these molecules form specific bridges allowing specific molecules to pass through
Transport across membranes The cell membrane is thin and provides a large
surface area for diffusion to occur Diffusion is the movement of molecules or ions
from a region of high concentration to a region of low concentration until they are spread out evenly (down a concentration gradient)
A big difference in concentration, an increase in temperature, small molecules and a short diffusion distance makes the rate of diffusion faster
Facilitated diffusion This allows faster movement It involves the use of proteins to assist (facilitate)
diffusion Specific channel proteins form pores for specific
molecules Carrier molecules bind to specific molecules,
change shape and deliver the molecule to the other side of the membrane
Osmosis This is the diffusion of water molecules They move from where they are in a high
concentration (a dilute solution) to where they are in a low concentration (a concentrated solution)
Osmosis in plant cells As water enters a plant cell, the cell starts to
swell. The cell wall starts to resist the stretching which creates pressure
When no more water can enter the cell, it is said to be TURGID. This provides strength and support to the cell
If water leaves a cell, the membrane can pull away from the cell wall. This causes a plant to wilt
Different solutions Solution – a mixture of 2 or more substances Solvent – the liquid that a substance dissolves in Solute – the substance that dissolves in a solvent Hypotonic – a weak solution: weaker in solute
concentration than cell Hypertonic – a strong solution: stronger in solute
concentration than cell Isotonic – a solution with the same concentration
as cell.
Active transport
Moving molecules against a concentration gradient (from low to high concentration)
It requires special carrier proteins called membrane pumps
It uses energy in the form of ATP
Endocytosis and exocytosis For molecules too large to pass through the
membrane Endocytosis – taking materials into the cell by
closing the cell membrane around it to form a vesicle (There are 2 types, pincytosis and phagocytosis)
Exocytosis – material in vesicles in the cell fuse with the cell membrane and are released