cell biology Flashcards
2 types of cell
Eukaryotic (with a nucleus eg, animal, plant and yeast cells) and prokaryotic (no nucleus - bacterial cells only)
which cells are biggest / smallest
Plant cells are the largest, followed by animal cells, yeast cells and finally bacterial cells are the smallest.
where is the dna in eukaryotic
Eukaryotic cells have their DNA inside a nucleus. The DNA is coiled up into structures called chromosomes.
where is the dna in prokaryotic
Prokaryotic cells have their DNA in the cytoplasm.
They have a single DNA loop, and may also have small rings of DNA called plasmids.
cell structures in eukaryotic cells
Cell membrane, cytoplasm, nucleus, mitochondria and ribosomes.
function of cell membrane
Controls entry and exit of substances (cell transport).
function of mitochondria
To carry out aerobic respiration and release energy (in the form of ATP) for cell activities. The more mitochondria, the more energy the cell needs.
function of ribosome
To carry out protein synthesis (making proteins). The more ribosomes, the more proteins the cell needs to make.
structures found in only plant / algal cells
Chloroplasts, large vacuole and cell wall made of cellulose.
function of chloroplasts
Chloroplasts absorb light energy to carry out photosynthesis and produce glucose for the plant.
The more chloroplasts, the more glucose a cell can make.
function of large vacuole
function of cell wall
Cellulose is strong and rigid. It strengthens the cell (this is important as plants do not have a skeleton to give them support).
only cell structures in prokaryotic
why dont prokaryotic cells have mitochondria
Mitochondria are bigger than prokaryotic cells so they don’t fit inside.
specialised cells
A cell that has a certain structure to help it carry out a particular function
examples of specialised animal cells
Sperm cells, nerve cells (neurones), muscle cells, glandular cells, epithelial cells.
examples of specialised plant cells
Root hair cells, xylem cells, phloem cells, palisade and spongy mesophyll cells.
stem cell
A cell that has not become specialised yet.
cell differentiation
The process during development where a stem cell develops to form a specialised cell.
when does differentiation happen
in animal cells, differentiation happens at an early stage (when the animal is an embryo), but in plants some cells can differentiate throughout the life of the plant.
where are stem cells in animals
Early stage embryos are completely made of stem cells, but in adults, the only place stem cells exist is in our bone marrow (inside large hollow bones, eg.
Thigh bone)
where are stem cells in plants
Meristem tissue is made of stem cells. It is found near the xylem and phloem, and also in the root and shoot tips.
why do scientists think animal stem cells are so useful
Stem cells can be made to differentiate into different types of cell. We can use them to treat diabetes and paralysis as well as use them for research into other disorders.
therapeutic cloning
Producing an embryo with the same DNA as a patient, so that stem cells can be used for medical treatment. The stem cells will not rejected by the patient’s body.
risks of using animal stem cells
Infections caused by viruses could be transferred.
Also some people have ethical objections for religious reasons (as embryos are destroyed during treatments and research).
why do scientists think plant stem cells are so useful
Stem cells can be used to clone plants quickly and cheaply. This can save rare species from extinction, or produce crop plants with resistance to disease for farmers.
microscope
A piece of equipment that uses lenses to magnify cells so that we can see some of their structures.
types of microscope
Light microscope (uses light to make an image) and electron microscope (uses electrons to make an image)
how have microscopes been developed over years
Lenses have improved now glass can be made without cracks or bubbles showing up. Also the electron microscope shows more detail than the light microscope.
why are electron microscopes better
Electron beams rather than light means resolution is better. So, more detail can be seen as we can get clearer images of sub-cellular structures at higher magnifications.
equation for magnification
Magnification = image size / actual size (Remember
this as |/ AM)
chromosomes
Structures in the nucleus, made of a chemical called DNA. They are normally found in pairs in body cells (one of each pair from Mum, and one from Dad).
genes
A small section of DNA (in a chromosome) that is the code for one whole protein. Ribosomes read the code and then make a protein by joining lots of amino acids together.
cell cycle
The life of a cell, including it growing and carrying out it’s functions and then replicating it’s DNA before getting ready to divide by mitosis to form new cells.
when does mitosis take place
When cells need to divide to grow or repair an organism. Adults do less mitosis as they are no longer growing, and only repairing tissues/ replacing old cells.
new cells from mitosis
Two genetically identical cells (identical to each other and to the parent cell that they came from).
3 types of cell transport
Diffusion, osmosis and active transport all move molecules in and out of cells.
diffusion
The spreading out of particles (molecules) in a solution or a gas, from an area of high concentration to an area of lower concentration. It is passive as it requires no energy.
factors affecting rate of diffusion
Concentration gradient
Temperature
Surface area of the membrane.
what molecules move into cell by diffusion
Oxygen and glucose are the two most important molecules that enter cells by diffusion. They are both needed for aerobic respiration.
what molecules move out of cells by diffusion
Carbon dioxide and urea are both removed as wastes from cells by diffusion - so they can be excreted by the lungs (COz) and kidneys (urea).
surface area to volume ratio
The larger the surface area compared to the volume of a cell or organism, the faster the rate of diffusion. It needs to be fast to allow enough molecules in/out for survival.
features of efficient exchange surfaces
Large SA and thin membrane (plus, in animals, efficient blood supply and ventilation).
which mammal surfaces are efficient
Small intestine and lungs.
which fish surfaces are efficient
Gills
which plant surfaces are efficient
Roots and leaves.
osmosis
The diffusion of water molecules from a dilute solution to a more concentrated solution across/through a partially permeable membrane.
active transport
The movement of substances (solutes) against their concentration gradient (from dilute to more concentrated). This requires energy from respiration, so it is active not passive.
why is active transport needed
When a cell needs molecules that it can’t get by diffusion, as there are more of the molecules in the cell than there are outside it. AT is the only way to get these molecules.
plant example of active transport
Allows mineral ions to be absorbed into root hair cells from very dilute solutions in the soil. Plants need these ions for healthy growth.
animal example of active transport
Glucose molecules in the small int. need to be absorbed into the blood. Most of the glucose diffuses, but when the concentration in the blood is higher than in the intestine, AT absorbs the rest.
how do bacteria reproduce
They reproduce by BINARY FISSION
how often can bacteria reproduce
As often as every 20 minutes
what can slow rate of bacteria reproduction
The two main factors are -
• Unsuitable temperature
• Not enough nutrients
how can we grow bacteria in a lab
They are grown on a nutrient gel called AGAR or in a solution called a NUTRIENT BROTH
aseptic technique
It’s a method of growing uncontaminated cultures of bacteria for study.
petri dish
A plastic or glass dish with a lid, filled with agar and used to grow bacteria.
why do we sterilise the agar and petri dish
When we sterilise the dish, all other bacteria are killed. this reduces contamination
how to transfer bacteria to petri dish
We use an inoculating loop.
how to sterilise inoculating loop
We pass the inoculating loop through a Bunsen flame.
once inoculated, petri dishes are stored upside down. why?
To prevent condensation forming on the agar surface and disturbing the bacteria.
what temp should bacteria be grown in at school
25’c
why are bacteria grown at 25’c in school and not 37’c
Bacteria which are dangerous to humans could grow
at 37°C
bacterial colony
A group of bacteria which have all grown from one original bacteria.
bacterial colonies are often in circular shapes. how do you find out its area
