Biology - B1
- Created by: abbiedye
- Created on: 20-06-18 08:46
What are cells?
- All living things are made of cells
- Eukaryotic cells are complex. All animal and plants cells are eukaryotic.
- Prokaryotic cells are smaller and simpler. Bacteria are prokaryotic cells.
Animal cell structure
- Cell membrane - holds the cell together - controls what goes in and out of the cell
- Cytoplasm - gel-like substance - where chemical reactions happen - contains enzymes
- Mitochondria - most of the reactions for aerobic respiraion take place - energy transferred
- Nucleus - genetic material - controls activities of the cell
- Ribosomes - where proteins are made
Plant cell structure
- All of the bits that animal cells have plus extra things
- Cell wall - made of cellulose - supports the cell and strengthens it
- Permanent vacuole - contains cell sap - (weak solution of sugars and salts)
- Chloroplasts - where photosynthesis occurs - makes food for the plant - contains chlorophyll - absorbs light needed for photosynthesis
Bacterial cell structure
- Bacteria don't have chloroplasts or mitochondria
- Cytoplasm
- Cell membrane
- Cell wall
- no 'true' nucleus - single circular strand of DNA - floats freely in the cytoplasm
- may also contain one or more small rings of DNA called plasmids
Explain Microscopy
- Light microscopes can be used to look at cells
- Electron microscpes have a higher resolution than light microscopes - more detail
- magnification = image size / real size
Cell differentiation and specialisation
- The process by which cells change to become specialised is called differentiation
- As cells change, they develop different subcellular structures
Examples of specialised cells
- Sperm cells take the male DNA to the egg
- Nerve cells carry electrical signals around the body
- Muscle cells contract (shorten)
- Root hair cells absorb water and minerals
- Ploem cells transport food and xylem cells transport water
How do specialised cells perform their functions?
- Sperm cells - long tail + streamlined head to swim - mitochondria - for energy - enzymes - digest through egg cell membrane
- Nerve cells - carry electrical signals - long branched connections - to cover distance and to form a network around the body
- Muscle cells - long + contain lots of mitochondria - so they have space to contract and the energy to do so
- Root hair cells - big surface area (long hairs) - for absorbing water and mineral ions
- Phloem cells - have very few subcellular structures - stuff can flow through them
- Xylem cells - hollow - stuff can flow through them - joined end to end
What are chromosomes?
- Chromosomes contain genetic information
- The nucleus of a cell contains chromosomes
- Chromosomes are coiled up lengths of DNA molecules
- Each chromosome carries a large number of genes
What is the cell cycle?
- Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle
- Multicellular organsims use mitosis to grow or replace cells that have been damaged
- The end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes
- There are two main stages of the cell cycle
What is the process of growth and DNA replication?
1. In a cell thats not dividing, the DNA is all spread out in long strings
2. Before it divides, the cell has to grow and increase the amount of subcellular structures
3. It then duplicates its DNA - so there's one copy for each new cell. The DNA is copied and forms x-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of the other
What is the process of mitosis?
- Once its content and DNA have been copied, the cell is ready for mitosis
1. The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
2. Membranes frm around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided.
3. Lastly, the cytoplasm and cell membrane divide.
Stem cells
- Cells differentiate to become specialised for their jobs
- Undifferentiated cells are called stem cells
- Embryonic stem cells could be used to replace faulty cells in sick people
Why are people against stem cell research?
- Some people are against stem cell research because they feel that human embryos shouldn't be used for experiments since each one is a potential human life
- Others thinks that curing existing patients who are suffering is more important than the rights of embryos
Diffusion
- Diffusion is the spreading out of particles from an area of higher concentration to an area of lower concentration
- For example, the smell of perfume diffuses through the air in a room
How are cell membranes clever?
- They're clever because they hold the cell together, BUT they let stuff in and out as well
- Big molecules (starch and proteins) can't fit through the membrane
- Larger surface area - faster diffusion rate
How do organisms exchange substances with environm
- Cells can use diffusion to take in substances from the environment such as oxygen
- How easy it is for an organsim to exchange substances with its environment depends on the organsim's surface area to volume ratio
Osmosis
- Osmosis is the movement of water molecules across a partially permeable membrane from a less concentrated solution to a more concentrated solution.
- A partially permeable membrane is one with very small holes in it - tiny molecules can pass through (water) - bigger molecules can't (sucrose)
Active transport
- allows the plant to absorb minerals from a very dilute solution against a concentration gradient (lower-higher)
- need energy from respiration
- Root hair cells - large surface area to absorb - concentration of minerals is higher in the cell than the soil
- human - lower concentration in gut and a higher concentation in blood - nutrients (glucose) taken into blood stream - AGAINST CONCENTRATION GRADIENT
Exchanging surfaces
- single-celled organisms - gases and dissolved substances can diffuse directly into/out of the cell or across the cell membrane- large surface area compared to their volume - enough substances can be exchanged
- multicellular organisms - smaller surface area compared to thir volume - not enough substances can diffuse from their outside surface to supply their entire volume - exchange surface structures have to allow enough of the necessary substances to pass through
How are exchange surfaces adapted?
- thin membrane - short distance to diffuse
- large surface area - lots of substances can diffuse at once
- lots os blood vessels (animals) - to get stuff into and out of the blood quickly
- gas exchange surfaces in animals are ventilated
Gas exchange in the lungs
- Oxygen and carbon dioxide are exchanged in the lungs
- The lungs contain millions of little air sacs called alveoli. This is where gas exchange happens.
- The alveoli are specialised for the diffusion of oxygen and carbon dioxide
Leaf structure and diffusion
- Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens
- Stomata - controlled by guard cells - losing water - open up
- Flattened shape - large surface area
- Oxygen ad water vapour diffuse out of the leaf
- Carbon dioxide diffuse into leaf
Fish gills and gas exchange
gills - the gas exchange in fish
Oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water
each gill - made of gill filaments (big surface area) - covered in lamellae
lamellae - increase surface area - lots of blood capillaries
blood - one direction and water in the opposite - LARGE CONCENTRATION GRADIENT
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