B1: Cells Flashcards
What are features of a light microscope?
Cheaper to make
Allow you to see the outline of cells
Uses light to form images
Living samples can be viewed
Low magnification
Low resolution
What are features of electron microscopes?
Can visualise finer details including organelles
Higher magnification
Higher resolution
Samples cannot be living
Use beam of electrons to form images
Expensive
What is the equation for magnification?
Magnification = image size / object (cell) size
How big are cells?
A few micrometers long
1 micrometer = 1x10^-6
How to you convert micrometers to mm?
Divide by 1000
Where is DNA found in eukaryotic cells?
In the nucleus
What are 2 examples of eukaryotic cells?
Animal cells
Plant cells
What are organelles?
Sub-cellular structures
Where is DNA in prokaryotic cells found?
A single loop of DNA
As plasmids (small loops of DNA)
What is an example of a prokaryotic cell?
Bacteria
What is the cell membrane?
Semi-permeable
Controls movement of substances in and out of a cell
What is the cell wall made of and what is it’s function?
Cellulose
Strengthens the cell
What takes place within the mitochondria?
Respiration to release energy
What is the function of ribosomes?
Site of protein synthesis
What are chloroplasts?
Made of chlorophyll that absorbs light energy for photosynthesis
What is stored within the permanent vacuole?
Cell sap
How do bacteria reproduce?
By binary fission
They divide every 10 minutes
How do we make cultures with aseptic technique?
-Lift lid of petri dish towards flame (to sterilise air by moving microbes away/killing them)
-Put drop of culture on agar/spread evenly
-Put drops/discs of antibiotics on culture if needed
-Few bits of tape (to allow aerobic respiration), incubate at 25 degrees celsius
-Measure size of cultures/areas with no bacteria with pi x r^2 or pi x d / 4
How many pairs of chromosomes do diploid cells have?
23
How many chromosomes are in gametes?
23
What is a haploid cell?
A cell with 23 singular chromosomes
Which process happens amongst cells for growth and repair?
Mitosis
What is the process of mitosis?
- Nucleus dissolves and genetic material is duplicated
- The two sets of chromosomes move to different sides
- Mitochondria, ribosomes & other organelles are duplicated
- The cell divides, producing two genetically identical diploid cells
(New nuclei are formed, or “the nucleus divides”)
What are stem cells?
Cells that can specialise to perform specific functions. They are found in animal embryos and plant meristems
Where are adult stem cells made?
In bone marrow
What type of cell can adult stem cells differentiate into?
Blood cells
What can embryo clones be used for?
To harvest stem cells
These can be used to treat conditions without them being rejected by the person’s body
Can differentiate into any type of specialised cell in the body
What can cloning plants be used for?
To preserve species
To produce crops with desired traits
What is diffusion?
The movement of particles from an area of high concentration to an area of low concentration (down the concentration gradient) through a partially permeable membrane
This is passive as it requires no energy
What is osmosis?
The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
This is a passive process
How can the rate of diffusion and osmosis be increased?
- Increasing the difference in concentrations (steeper concentration gradient)
- Increasing the temperature
- Increasing the surface area of the membrane
What is the practical for osmosis?
- Weigh, and place identical cylinders from a potato in sugar solutions of varying concentrations
- After set time, remove excess water and reweigh
- Calculate % change in mass = (final mass - initial mass / initial mass) x 100
- Plot % change in mass against concentration. Using the line of best fit, the concentration at 0% change in mass is the same as inside the vegetable
What is active transport?
The movement of particles from a more dilute solution to a more concentrated solution
This requires energy (from respiration), and so can move them against the concentration gradient
What is the cytoplasm?
Jelly-like substance
Where chemical reactions happen
What is the function of sperm cells?
To fertilise an ovum (egg)
What are adaptations of sperm cells?
- Tail to swim to the ovum and fertilise it
- Lots of mitochondria to release energy from respiration, enabling the sperm to swim to the ovum
What is the function of red blood cells?
To transport oxygen around the body
What are adaptations of red blood cells?
- No nucleus so more room to carry oxygen
- Contains a red pigment called haemoglobin that binds to oxygen molecules
- Flat bi-concave disc shape to increase surface area-to-volume ratio
What is the function of muscle cells?
Contract and relax to allow movement
What are adaptations of muscle cells?
- Contains protein fibres, which can contract to make the cells shorter
- Contains lots of mitochondria to release energy from respiration, allowing the muscles to contract
What is the function of nerve cells?
Carry electrical impulses around the body
What are adaptations of nerve cells?
- Branched endings, called dendrites, to make connections with other neurones or effectors
- Myelin sheath insulates the axon to increase the transmission speed of the electrical impulses
What is the function of root hair cells?
Absorb mineral ions and water from the soil
What are adaptations of root hair cells?
- Long projection speeds up the absorption of water and mineral ions by increasing the surface area of the cell
- Lots of mitochondria to release energy for the active transport of mineral ions from the soil
What is the function of palisade cells?
Enable photosynthesis in the leaf
What are adaptations of palisade cells?
- Lots of chloroplasts containing chlorophyll to absorb light energy
- Located at the top surface of the leaf where it can absorb the most light energy
What are advantages of adult stem cells?
- Fewer ethical issues - adults can consent to have their stem cells removed and used
- An established technique for treating diseases such as leukaemia
- Relatively safe to use as a treatment and donors recover quickly
What are disadvantages of adult stem cells?
- Requires a donor, potentially meaning a long wait time to find someone suitable
- Can only differentiate into certain types of specialised cells, so can be used to treat fewer diseases
What are advantages of embryonic stem cells?
- Can treat a wide range of diseases as can form any specialised cell
- May be possible to grow whole replacement organs
- Usually no donor needed as they are obtained from spare embryos from fertility clinics
What are disadvantages of embryonic stem cells?
- Ethical issues as the embryo is destroyed and each embryo is a potential human life
- Risk of transferring viral infections to the patient
- Newer treatment so relatively under researched - not yet clear if they can cure as many diseases as thought
What can plant meristems do?
Differentiate into all cell types - they can be used to create clones of whole plants
What are advantages of plant meristems?
- Rare species of plants can be cloned to prevent extinction
- Plants with desirable traits, such as disease resistance, can be cloned to produce large numbers of identical plants
- Fast and low-cost production of large numbers of plants
What are disadvantages of plant meristems?
- Cloned plants are genetically identical
- A whole crop is at risk of being destroyed by a single disease or genetic defect
What is the process of therapeutic cloning?
- Cells from a patient’s body are used to create a cloned early embryo of themselves
- Stem cells from this embryo can be used for medical treatments and growing new organs
- These stem cells have the same genes as the patient, so are less likely to be rejected when transplanted
