Biology- Cells

Prokaryotes and Eukaryotes

• A cell is either one or the other of these
• Eukaryotic cells are complex and inculde all animal and plant cells
• Prokaryotic cells are simpler and smaller - bacteria
• Eukaryotes are organisms made up of many eukarotic cells
• Prokaryotes is a single-celled organism

Plant and animal cells - have differences and similarities

Bacterial cells

• They are prokaryotes
• They are very small cells
• They don't have a nucleus but instead a singular strand of DNA and often a plasmid.

What is it used for?

• Microscopes let us see things that we cant see in the naked eye, like the cells structure and detail.

Light microscopes

• Use light and lenses to form an image of a specimen and magnify it. 
• Let us see large subcellular structures, like nuclei

Electron microscopes

• Use electrons instead of light
• Have a much higher magnification and higher resolution than light microscopes.
• Let us see smaller things, like the internal structure of mitochondria and chloroplasts as well as ribosomes and plasmids

Magnification

This allows us to work out the size of the objects from photos as well as how much an image has been magnified.

Sperm cells - Reproduction

• Function - to get the male DNA to the female DNA.
• Adaptions - has a long tail and a streamlined head to help it swim to the egg, has a lot of mitochondria to give it energy, carries enzymes to digest throught the egg cell membrane.

Nerve cells - Rapid signalling

• Function - to carry eectrical signals from one part of the body to another.
• Adaptions - long to cover disance, has branched connections at the end to connect to other nerve cells and form a network through the body.

Muscle cells - Contraction

• Function - to contact quickly.
• Adaption - long so they have space to contract, contain lots mitochondria to produce energy needed for contraction.

Root hair cells - absorbing water and minerals

• Function - on surface of plant roots to absorb water and minerals from the soil
• Adaptions - long 'hairs' that stick into the soil.

Phloem and Xylem cells - transporting substances

• Function - to transport substances like food and water around a plant.
• Adaptions - form tubes, the cells are long and join end to end. Xylem cells are hollow to allow water pass through them and Phloem cells have few subcellular structures also so stuff can' flow through them.

What are chromosomes?

• They contain genetic information.
• They are coiled up lengths of DNA molecules.
• They each carry a large number of genes - different genes control different characteristics.
• Body cells normally carry 2 copies of each chromosome, one from the mother and the other form the father.
• A human cell has 23 pairs of chromosomes.

The Cell Cycle - Growth, Development and Repair

• Organisms divide to provide new cells
• When cells divide its called mitosis.
• Multicellular organisms use mitosis to grow and replace damaged cells.
• This leaves two new cells, identical to the original.

Growth and DNA replication

• Before a cell divides the cell increases the amount of subcellular structures it has.
• It then duplicates the DNA, and forms an X-shaped chromosome.

Mitosis

• The chromosomes get pulled apart by cell fibres.
• Membranes from around each set of the chromosomes, these become the nuclei of the two new cells.
• Then the cytoplasm and cell membrane divide.
• This process produces two new daughter cells, these contain the exact same DNA as the previous cells as well as being identical to the parent cell.

What are Stem cells?

• They are cells that can turn into any type of cell.
• Stem cells can divide to produce lots more undifferentiated cells, depending on the instructions they're given.
• They are found in early human embroyos .
• Adults stem cells are found in certain places like bone marrow, unlike embryonic stem cells they cant turn into every cell.
• They can be used to create clones.

• Differentiation is the process when a cell becomes specialised for its job
• Different cells develop different subcellular structures which allows them to carry out specific functions
• In animal cells the ability to differentiate is lost at an early age
• Plant animals never lose this ability
• Cells that differentiate in mature animals are used for replacing and repairing cells-skin or blood cells
• Stem cells don't differentiate

Cells make up all living organisms

Tissues

a group of similar cells that work together to carry out a particular function. It can include more than one type of cell.

• Examples of tissues - Muscular tissue, to contract and move whatever its attatched to                                 - Glandular tissue, to make and secrete chemicals                                 - Epithelial tiisue, to cover parts of the body

Organs

an organ is a group of different tissues that work together to perform a certain function

The different tissues work together doing important roles, like in the stomach the muscular tissues churn up the food.

An organ system is a group of organs working together to perform a particular function.

An example of a organ system is the digestive system which breaks down and absorbs the food of a mammal. It's made up of these organs- Glands, which produce digestive juices                                                                - Stomach and small intestine, which digest food                                                                - Liver, which produces pile                                                                - Small intestine, which absorbs soluble food molcules                                                                - Large intestine, absorbs water from undigested food

• Enzymes are catalysts produced by living things
• Reduce the need for high temperatures and used to speed the useful chemical reactions inside the body
• Enzymes are large proteins and all made up of chains of amino acids. These chains get folded into unique shapes need to do their jobs
• Enzymes have an active site that fits into a unique substance involved in a reaction
• They only catalyse one specific reaction

Lock and key model

Rate is a measure of how much something changes over time.

To work out the rate of reaction you can use the formula, rate = 1000 divided by time.

If an experiment measures how much something changes over time, you calculate the rate of reaction by dividing the amount taht it has changed by the time taken

• Respiration using oxygen
• Most efficent way to transfer energy from glucose
• Goes on all the time in plants and animals
• Most of the reactions in aerobic respiration happen inside mitochondria
• Provides most of the energy needed by people and animals - moving, keeping warm etc.

glucose + oxygen ------ carbon dioxide + water

                    +              -------               +           

• Used when ypur body cant supply oxygen to your muscles quick enough during vigourous exercise
• The incomplete breakdown of glucose, making lactic acid
• Doesnt transfer anywhere near the same amount of energy as aerobic respiration, because the glucose isnt oxidised.
• Only useful in emergencies - during exercise when it allows you to move your muscles for longer

glucose -------- lactic acid

Plants and yeast

• Anaerobic respriation in these produce ethanol too
• Anaerobic respiration in yeast cels is called fermentation
• Fermentation by yeast is used to make products like bread and bear and wine

glucose ------- ethanol + carbon dioxide