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Flashcards in B1 Cell Biology Deck (38):

Use the terms 'eukaryotic' and 'prokaryotic' to desrcibe types of cells

- Cells can be either prokaryotic or eukaryotic
- Eukaryotic cells are complex, animal and plant cells -> eukaryotes are organisms made up of eukaryotic cells
- Prokaryotic cells are smaller and simpler, bacterial cells -> a prokaryote (single-celled organism)


Describe the features of bacterial (prokaryotic) cells

- Loop of genetic material that isn't bound within a nucleus, freely 'swimming' within cell, copied in binary fission
- One or more plasmids: small loops of DNA that are passed between bacteria/species and can result in antibiotic resistance
- Ribosomes, Cytoplasm, Cell Membrane, Cell Wall
- If bacteria lives in water = flagellum, helps bacteria move in water
- If bacteria lives in air = slime capsule, so the cell doesn't dry out


Recall the structures found in animal and plant cells

- Nucleus: genetic material, controls cell
- Mitochondria: release energy from glucose in aerobic respiration (which happens there)
- Cytoplasm: holds the cell shape, the site of where most of the chemical reactions take place (enzymes control reactions)
- Cell Membrane: semi-permeable so controls what goes in and out the cell and keeps the cell together
- Ribosomes: make proteins

- Has all the structures of an animal cell
- Cell Wall: made up of cellulose, protects and strengthens the cell
- Vacuole: filled with cell-sap and the water availability determines shape
- Chloroplasts: contain the green pigment chlorophyll which absorbs light for photosynthesis (happens in the chloroplasts)


What are the sizes of eukaryotic and prokaryotic cells

Animal Cell: 10μm-30μm
Plant Cell: 10μm-100μm
Bacterial Cell: 1μm

Estimating area of a subcellular structure: area = length x width


Required Practical: Using a light microscope (preparation of slides)

Animal material:
1a) Using a cotton bud swab the inside of persons cheek to extract cells
2a) Rub the cotton bud onto the centre of a clean microscope slide
3a) Add a drop of methylene blue stain

Plant Material:
1b) Using tweezers peel off a single layer of onion skin
2b) Lay flat on of a clean microscope slide
3b) Add a drop of iodine

4) Avoiding air bubbles and using a mounted needle, slowly lower a coverslip over the stain
5) View under a light microscope at low power and then increase the magnification


How do you calculate magnification?

magnification = image size (on the paper) / actual size


Compare electron and light microscopes

Light microscopes:
- cheap
- portable
- can view live specimen
- low magnification/resolution

Electron microscopes:
- more detailed image (0.2nm resolution)
- only able to view dead specimen
- expensive
- not portable


Explain the conversions for measurements

m -(x1000)-> mm -(x1000)-> μm -(x1000)-> nm
nm -(÷1000)-> μm -(÷1000)-> mm -(÷1000)-> m


Describe what is meant by differentiation and a specialised cell

- Differentiation is the process by which a cell changes to become specialised for its jobs
- Different subcellular structures are developed and turn into different types of cells for a specific function


Specialised animal cell: Sperm Cell

- Function is to travel towards and fertilise an egg
- Long tail and streamlined head help it to swim
- Nucleus contains half of the full chromosomes
- Lots of mitochondria in the cell to transfer energy to the tail
- Acrosome in the head contains enzymes to break through the eggs outer layer


Specialised animal cell: Nerve Cell

- Function is to carry electrical signals around the bodies of animals
- Dendrites: makes connections with other nerve cells
- Axon: long, conducts electrical impulses in one direction
- Myelin Sheat: insulates the impulse
- Synapses: sends neurotransmitter chemicals to another nerve cell or effector
- Many mitochondria in the synapses to transfer energy needed to make the transmitter chemicals


Specialised animal cell: Muscle Cells

- Function is to contract and relax
- Striated muscle cells found in the muscles that enable the body to move
- Smooth muscle cells found in the tissues in the digestive system to move food in the gut
- Striated muscle cells contain:
* special proteins that slide over each other
* many mitochondria to transfer the energy needed for chemical recations
* a store of glycogen that can be broken down and used in respiration to transfer energy


Specialised plant cell: Root Hair Cells

- Function is to absorb water and mineral ions from the soil (close to xylem tissue so substances can be transported through the plant)
- Increased SA of the root hair so that the cell can absorb water and mineral ions efficiently
- Large permanent vacuole which speeds up the movement of water by osmosis from the soil into the root hair cell
- Many mitochondria which transfers energy needed for active transport of mineral ions into the cell


Specialised plant cell: Photosynthetic cells

- Plants that can make their own food by photosynthesis
- Chloroplasts contains chlorophyll to trap the light needed
- Found in continuous layers in the leaf and outer layers of the stem
- Large permanent vacuole that helps keep the cell rigid


Specialised plant cell: Xylem Cell

- 2 main functions
1 = transport water and mineral ions from the roots to the stem and the leaves (transpiration)
2 = xylem tissue supports the cell
- Living when they're first formed, then a chemical called lignin builds up in spirals in the cell walls
- Cells die forming hollow tubes where water and mineral ions can move up
- Lignin strengthens the tubes


Specialised plant cell: Phloem Cell

- Function is too transport the products of photosynthesis to the rest of the plant from the leaves
- Made from living cells where the cell wall has broken down between to form sieve plates that allow sugars to flow freely by translocation
- Companion cells are found either side of the phloem cells that have many mitochondria to transfer energy to phloem cells


Describe how bacteria reproduce and the conditions required

- Bacteria replicate by binary fission
* circular DNA and plasmids replicate
* cell increases in size and the DNA and plasmids move to opposite ends of the cell
* cytoplasm begins to divide and new cell walls begin to form
* cytoplasm divides creating two new daughter cells, each new daughter cell has one copy of circular DNA , but variable numbers of plasmids

- Warm (not too hot as it will kill the bacteria) and aerobic conditions - sometimes like lots of nutients


Describe how to prepare an uncontaminated culture

- Disinfect desk and wash hands to kill any extra unwanted bacteria
- Sterilise inoculating loop with a busen burner and transfer bacteria broth onto the agar jelly
- Petri dish should be lightly taped to stop microbes from the air entering, but still allows for the flow of air
- Petri dish stored upside down to stop drops of condensation falling onto the agar surface
- Allow bacteria to grow for 2 days at 25 degrees max so the risk of growing harmful bacteria is low

* eventually the growth of bacteria will stop because of limiting factors, for example: lack of food/lack of space/toxins, and eventually the population will die due to L.F


Calculating cross sections or clear areas around colonies (+ effect of antibiotics and antiseptics on bacterial growth)

- Clear areas = inhibition zones from antiseptics or antibiotics
- A control paper disc (not soaked in an antibiotic, but in sterile water) must be used to show that the clear area is due to the antibiotic only
- Measure the diameter of the inhibition zone and calculate the area
- Also can be used to measure the size of a bacterial colony


How to calculate the number of bacteria in a population

- Divide the total time that the bacteria are producing cells by the mean division time, this gives u the number of divisions
- Use number of divisions as the power of 2


Describe how genetic information is stored in the nucleus of a cell

- Nucleus of each cell contains the genetic material in the form of chromosomes
- Chromosomes are coiled lengths of DNA molecules
- Each chromosome carries lots of genes, genes control the development of different characteristics
- There are 2 of each chromosome, one from the mother and one from the father
- There are 23 pairs and 46 total chromosomes (pair 22 and then X and Y chromosomes)


Describe the processes in the cell cycles

- cell grows and increases the number of subcellular structures
- DNA is replicated, one copy for each cell
- DNA is copied and forms X-shaped chromosomes, each arm is an exact duplicate

- chromosomes line up in the centre of the cell and cell fibres then pull them apart (each arm of DNA goes to opposite sides)
- membranes form around each set of chromosomes
- these become nuclei of 2 new cells - nucleus has dividied
- lastly cell membrane and cytoplasm divide
- cell has produced 2 new daughter cells which contains the exactly same DNA as parent cell, identical


What is a stem cell?

- A stem cell is an undifferentiated cell that is capable of becoming other cell types
-> when a cell differentiates it produces certain subcellular structures to become specialised and is adapted for that function


What are the sources of stem cells?

Embryos, Adult Cells (skin cells + bone marrow) and cuttings from plants to create genetically identical plants


What are the roles of stem cells?

- Modern medicine uses adult stem cells to cure diseases , e.g. stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells of patient -> someone with lukemia
- Embryonic stem cells used to makes insulin-producing cells for people with diabetes, could even replace nerve cells for people who are paralysed


Describe the advantages and disadvantages of stem cell research

- embryonic cells are totipotent
- some believe that curing patients that already exist and who are suffering is more valid
- embryos used are usually unwanted ones from fertility clinics, do if the blastocysts weren't used in research they would be destroyed anyway, should put them to use
- therapeutic cloning

- some believe that the embryo has the right to life
- unable to consent
- if given to a patient they must be on drugs for the rest of their life to stop rejection of the body


Describe how plant stem cells are created

- in plants cells have the ability to become totipotent again (e.g. in the leaf)
- cutting is taken - cells become meristem cells again (growing part)
- end is dipped into growth powder
- put into compost to grow, grows roots to collect minerals and water
- eventually grows into a genetically identical plant of the parent plant (a clone)
- method used by farmers


Describe how embryonic stem cells are created

- a zygote (fertilised egg with a full set of 46 chromosomes) divides by mitosis
- this forms the embryo where all the cells are totipotent (have the potential to become any cell) - are undifferentiated
- embryo will undergo the first wave of differentiation forming the structure blastocyst
- outer cells have the ability to become the cells that form the placenta and umbilical cord
- inner cell mass cells have the genes to create the human itself, have the potential to become most cells in the body, these are the cells used to treat illnesses (the stem cells used)


Describe the process of therapeutic cloning

- cloning a human embryo to be genetically identical to the patient, so you can harvest stem cells from it to treat patient
- zygote is formed from the nucleus of the patient (their full chromosomes) and the egg from a donor
- small electric shock given to the egg so it forms an embryo, therefore cells become totipotent
- in a petri dish each cell can be programmed individually to differentiate to treat the patient's disease (e.g. nerve cells for paralysis)


Describe the process of diffusion including examples

- Diffusion is the net movement of particles in a solution or a gas from an area of high concentration to a lower concentration

Diffusion in the lungs (in the alveoli):
- Blood from the body from circulation in the capillary has a low conc of O2, high conc of CO2
- Air flowing in from ventilation has a high conc of O2, low conc of CO2
- CO2 will diffuse out of blood into alveoli and O2 will diffuse from the alveoli into the blood
- to maximise diffusion: a steep concentration gradient is kept by ventilation and circulation, large surface area from spherical shape and a short diffusion distance of 1 cell

Diffusion in the digestive system (villi):
- from the lumen of the small intestine soluble food molecules are absorbed into the blood by the villi
- to maximise diffusion: continuous blood flow (molecules absorbed faster), large surface area from villi itself and short diffusion distance of 1 cell


What are the factors affecting diffusion?

The concentration gradient, temperature and SA:V (small ration = problems for diffusion)


Explain how SA:V relates to single-celled and multicellular organisms

- In single-celled organisms gases and dissolved substances can diffuse directly into or out of the cell across the cell membrane
- They have a large SA:V ratio so enough substances can be exchanged across membrane to supply the volume of cell
- Multicellular organisms have a small SA:V, not enough substances can diffuse from their outside to supply the entire volume
- So they need exchange surfaces for efficient diffusion (gas exchange in the lungs and villi in digestive system)


Explain how the effectiveness of an exchange surface can be increased

Small intestines -> villi increase SA so food is absorbed much more quickly into the blood
Lungs -> shape of alveoli maximises the diffusion of CO2 and O2
Gills -> gill filaments gives a big SA for the exchange of gases (O2 from the water diffuses into the blood in the gills and CO2 from the blood diffuses out into the water) and it's covered with lamellae which increases SA even more
Leaves -> flattened shape of the leaf increases the area of the exchange surface so it becomes more effective


Describe osmosis

- Osmosis is the net movement of a solvent (i.e water) from an area of high concentration to a lower concentration though a semi-permeable membrane

Plant cells in...
- A dilute solution -> vacuole swells -> whole cell will swell and become turgid
- Isotonic solution -> cell maintains brick-like shape -> cell can stack upright = more sunlight
- Concentrated sugar solution -> water moves out of cell shrinking vacuole -> not enough pressure against cytoplasm so it moves inwards -> plasmolysed

Animal cells (e.g. blood cells) in...
- A dilute solution -> becomes turgid and may burst as there is no cell wall to protect the cell
- An isotonic solution -> a blood cell would maintain biconcave shape (isotonic = normal state in the body)
- A concentrated solution -> water would move out of cell -> lose shape and become ineffeciant


What are the key steps and the variable of required practical 3?

Key steps:
- weigh potato chip before its put in solution
- dry off throughly, not measuring mass of extra moisture

I.V: concentration of solution
D.V: % change in mass of potato chip
C.V: surface area of chip, time left in solution, variety of potato


Describe the process of active transport including example

- Active transport is the movement of a substance from a low concentration to a high concentration (against the concentration gradient) using energy from respiration

Root Hair Cells:
- water will diffuse in by osmosis as there is always a low concentration in cell as water is continuously moved up the plant via transpiration
- cells have a higher concentration of mineral ions than the soil and the plant needs ions for growth
- proteins on cell membrane act as pumps -> collect minerals from the soil and twist them into the cell itself
- for the proteins to twist round energy is used from respiration

In the villus:
- glucose will pass into the bloodstream until it exceeds the equilibrium and there is a high concentration of glucose in the blood
- proteins in the villus membrane push glucose into bloodstream


Explain the differences between diffusion, osmosis and active transport

Diffusion is the net movement of a substance from a high concentration to a low concentration, until equilibrium is reached

Osmosis is the movement of water from a high concentration to a low concentration through a semi-permeable membrane

Active transport is the movement from a low concentration to high concentration using energy from respiration 9not passive)


Why does mitosis occur?

Mitosis occurs for...
- cell growth (organism)
- replacing damaged cells
- repair damaged tissues
- asexual reproduction