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