Cell structure

Cells

Smallest unit of living matter, they make up all living things; plants, animals.

Eukaryotic cells

Has a true nucleus as well as a cellulose cell wall. Ex = Animal cells, plant cells

Animal cells

Average size = 10-30 pm. Has cell membrane, ribosomes, mitochondria, cytoplasm and nucleus.

Plant cells

Average size = 10-100pm. Has cell wall, cell membrane, mitochondria, chloroplast, cytoplasm and vacuole.

Cell wall

Provides support and maintains shape of the plant cell.

Vacuole

Gives extra support and makes the cell turgid when it's filled with water.

Chloroplasts

Enable the plant cell to absorb light energy so the plant can make it's own food through photosynthesis.

Nucleus

Contains all the genetic information and controls the activities of the cell.

Mitochondria

Provides energy through respiration to carry out cellular activities.

Ribosomes

Where protein synthesis occurs.

Cytoplasm

Solvent where chemical reactions take place.

Algal cells

Aquatic organisms sharing similar features with plant cells. Classified as protists.

Algal cells

Contains chloroplasts so they can make their own foods through photosynthesis and cell wall made of cellulose that strengthens the cell and gives support and contains a nucleus

Prokaryotic cells

No true nucleus visible, DNA organised in loops. Average size = 0.2-2pm. Ex = Bacterial cells.

Bacteria

Single celled microorganisms, contains cytoplasm, membrane and cell wall. No genes in nucleus, no mitochondria or chloroplast. DNA in plasmid.

Eukaryotic vs prokaryotic

Eukaryotic cells has DNA in linear chromosomes and located in nucleus. Prokaryotic cell has DNA in circular chromosomes and no nucleus.

nm -> pm -> mm -> cm

10,000,000 nm = 1cm

10,000 pm = 1cm

10 mm = 1cm

Magnification

how much bigger the image of a sample is relative to it's actual size.

Calculation of magnification

size of image/actual size

Resolution

Ability of microscope to distinguish 2 separate items. The shortest distance between 2 objects that can be distinguished by an observer as separate entities. The clarity of a magnified objects that affects how much detail it can show.

Light Microscope

Cheap, widely used. Light supply. Basic source = light source, a lens and human eye. Compound microscopes use 2/more lenses to focus the light and obtain high magnification. Max resolution = 200nm. Max magnification = 2000x. Oil immersion lens reduces refraction, used when high resolution is required.

Electron microscope

Electron supply. Electrons deflected easily so specimen must be viewed in a vacuum which means they are dead/abiotic. Specimen is completely dehydrated, fixed in plastic and stained with an electron-dense chemical like lead, osmium or gold.

TEM

Transmission electron microscope. Used to view ultra thin sections of cells.

SEM

Scanning electron microscope. Scans an electron beam onto surface of a specimen and collects electrons reflected from the surface. 3-D images.

Electron microscope

Expensive and difficult to use. Large and time consuming. Electron beam. Magnification is 2000,000x. Resolution is 0.25nm.

Calculation of Image Size

Magnification x real size

Calculation of magnification

Image size / real size

Calculation of real size

Image size / magnification

Cell differentiation

As an organism develops, cells differentiate to form different types of specialised cells.

Cell differentiation and specialisation

Most animals differentiate at an early stage of development, whereas many types of plant cells retain the ability to differentiate throughout life. As a cell differentiates, it gets different sub-cellular structures that enables it to carry out a particular function. It has become a specialised cell.

Specialisation

Some specialised cells, such as egg and sperm cells, work individually. Others are adapted to work as part of a tissue, an organ or a whole organism

Examples of specialised animal cells

Nerve cells, Muscle cells, Sperm cells, Red blood cells.

Examples of specialised plant cells

Root hair cells, Xylem cells, Phloem cells.

Nerve cell

Specialised to carry electrical impulses around the body of an animal.

Adaptations of nerve cells

Lots of dendrites. Axon carries the nerve impulse, it can be very long. Synapse are adapted to pass the impulses to another cell. Dendrites to make connections to other nerve cells.

Muscle cell

Specialised cells that can contract and relax. Striated muscle cells work together n tissues called muscles. Muscles contract and relax in pairs to move the bones of the skeleton. Smooth muscle cells contact and squeeze the food through the gut.

Adaptations of nerve cells

Special proteins that slide over each other making fibres contract. Mitochondria transfer energy needed for chemical reactions that take place as the cells contract and relax. Stores glycogen, chemical that can be broken down and used in cellular respiration by the mitochondria to transfer energy needed for fibres to contract.

Sperm cells

Released a long way from the egg they are going to fertilise, contains genetic information from the male parent.

Adaptations of sperm cells

Long tail helps move sperm through female reproductive system. Middle section full of mitochondria, transfer energy needed for the tail to work. Acrosome stores digestive enzymes for breaking down the outer layers of the egg. A large nucleus contains the genetic information to be passed on.

Red blood cells

Packed with haemoglobin (protein) which binds oxygen in the lungs and releases oxygen in the tissues.

Adaptations of RBC's

No nucleus so that they can hold more oxygen (space for haemoglobin). Biconcave shape for a larger surface area so gas diffusion is quicker and easier. Biconcave shape to fit easily through capillaries.

Root hair cells

Root hair cells are close to the tips of growing roots, plants need to take in lots of water and dissolved mineral ions. Close to the xylem tissue. Mineral ions into the cell by active transport.

Adaptations of root hair cells

Greatly increase surface area available for water to move into the cell. Large permanent vacuole that speeds up movement of water by osmosis from the soil across the root hair cell. Mitochondria transfer energy needed for the active transport of mineral ions into root hair cells.

Xylem cells

Transport tissue in plant that carries water and mineral ions from the roots to the highest leaves and shoots. Supports the plant.

Adaptations of xylem cells

Alive when first formed, lignin builds up in spirals in cell walls and cells die to form hollow tubes that allow water and mineral ions to move easily through them, from one end of the plant. Spirals and rings of lignin in the xylem cells make them very strong and help them withstand the pressure of water moving up the plant. They also help support the plant stem.

Phloem cells

Carries food made by photosynthesis around the body of the plant. Made up of phloem cells that form tubes rather like xylem cells, but phloem cells don't become lignified and die. Dissolved food can move up and down the phloem tubes to where it is needed.

Adaptations of phloem cells

Cell walls between cells break down to form special sieve plates. These allow water carrying dissolved food to move freely up and down the tubes to where it is needed. Phloem cells lose alot of their internal structures but they are supported by companion cells that help to keep them alive. The mitochondria of the companion cell transfer the energy needed to move more dissolved food up and down the plant in the phloem.