unit 2A - cell structure

Question 1

what is found in a plant cell

Answer 1

1. smooth endoplasmic reticulum
2. cytoplasm
   3.nucleolus
   4.ribosomes
   5.cell wall
3. vacuole
4. Golgi apparatus
5. mitochondrion
6. plasmodesma (channels for exchanging substances with adjacent cells)
7. rough endoplasmic reticulum
8. chloroplasts
   12.plasma cell surface membrane
9. nucleus

Question 2

what is found in an animal cell

Answer 2

1. lysosome
2. ribosome
3. nucleus
4. Golgi apparatus
5. cytoplasm
6. mitochondrion
7. smooth endoplasmic reticulum
8. rough endoplasmic reticulum
   9.plasma (cell surface) membrane
   10.nucleolus

Question 3

description and function of a cell surface membrane

Answer 3

fount on the surface of animal cells and just inside the cell walls of other cells. it is made of mainly lipids and proteins.

it regulates the movement of substances into and out of the cell. it also has receptor molecules on it, which allows it to respond to chemicals like hormones.

Question 4

description and function of a nucleus

Answer 4

a large organelle surrounded by a nuclear envelope (double membrane) which contains many pores. the nucleus contains chromosomes (which some are made from protein bound linear DNA) and one or more structure(s) called the nucleolus.

the nucleus controls the cells activities. DNA contains instructions to make proteins. the pores allow substances to move between the nucleus and the cytoplasm. the nucleolus makes ribosomes.

Question 5

description and function of a mitochondria

Answer 5

usually an oval shape. they have a double membrane - the inner one is folded from the structures called cristae. inside the is the matrix, which contains enzymes involved in respiration.

It is the site of aerobic respiration, where ATP is produced. they’re found in large number of cells that are very active and require a lot of energy.

Question 6

description and function of a Golgi apparatus

Answer 6

a group of fluid-filled, membrane-bound flattened sacs. vesicles are often seen at the edges of the sacs.

it processes and packages new lipids and proteins. it also makes lysosomes.

Question 6

description and function of a golgi vesicle

Answer 6

a small fluid-filled sac in the cytoplasm, surrounded by a membrane and it is produced by the Golgi apparatus. (found around the golgi apparatus)

it stores lipids and proteins made by the Golgi apparatus and transports them out of the cell via the cell surface membrane.

Question 7

description and function of a rough endoplasmic reticulum (RER)

Answer 7

a system of membranes enclosing a fluid-filled space. the surface is covered in ribosomes.

it folds and processes proteins that have been made at the ribosomes.

Question 7

description and function of a lysosome

Answer 7

a round organelle surrounded by a membrane, with no clear internal structure.

they contain hydrolytic enzymes. these are kept separate from the cytoplasm by the surrounding membrane, and they can be used to digest invading cells or to break down worn out components of the cell.

Question 8

description and function of a smooth endoplasmic reticulum (SER)

Answer 8

similar to rough endoplasmic reticulum but with no ribosomes.

synthesises and processes lipids

Question 8

description and function of a ribosome

Answer 8

a very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. it is made up of proteins and RNA. its not surrounded by a membrane.

the site where proteins are made

Question 8

description and function of a cell wall

Answer 8

a ridged structure that surrounds cells in plants, algae and fungi. in plants and algae its mainly made of carbohydrate cellulose. in fungi its made of chitin

supports cells and prevents them changing shape

Question 9

description and function of a cell vacuole

Answer 9

a membrane-bound organelle found in the cytoplasm of plant cells. it contains cell sap - a weak solution of sugars and salts. the surrounding membrane is called the tonoplast

it helps maintain pressure inside the cell and keep the cell ridged. this stops plants wilting. its also involved in the isolation of unwanted chemicals inside the cell.

Question 10

description and function of a chloroplast

Answer 10

a small, flattened structure found in plants and algal cells. its surrounded by a double membrane, and also has membranes inside called thylakoid membranes. these membranes are stacked up in some part of the chloroplasts to form grana. grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.
the site where photosynthesis takes place. some parts of photosynthesis happens in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts)

Question 11

what’s an example of a specialised cell to carry out its specific function.

Answer 11

Epithelial cells
found in the small intestine and are specialised to absorb food efficiently

1. the walls of the small intestine have lots of finger like projections called villi. these increase surface area for absorption
2. the epithelial cells on the surface of the villi have folds in the cell-surface membranes, called microvilli. microvilli increases the surface area even more.
3. they also have lots of mitochondria - to provide energy for the transport of digested food molecules into the cell.

Question 12

how are tissues formed and what do groups of tissues form?

Answer 12

in multicellular eukaryotic organisms, specialised cells are grouped together to form tissues. a tissue is a group of cells working together to perform a particular function. different tissues work together to form organs. different organs make up organ systems.

example: epithelial cells make up epithelial tissue. epithelial tissue, muscular tissue and glandular tissue (which secretes chemicals) all work together to form the stomach. the stomach is part of the digestion system (organ system and digestion also involves small/ large intestine and liver)

Question 13

what are the 7 features and some functions of a prokaryotic cell?

Answer 13

1) the cytoplasm of a prokaryotic cell has no membrane-bound organelles. it has ribosomes but they’re smaller than those in a eukaryotic cell.
2) Like a eukaryotic cell, the plasma membrane is mainly made out of lipids and proteins which controls the movement of substances into and out of the cell.
3)the cell wall supports the cell and prevents it from changing shape. its made of a polymer called murine. murein is a glycoprotein (a protein with a carbohydrate attached to it)
4) some prokaryotic cells (eg bacteria) have a capsule made up of secreted slime. this helps to protect bacteria from attack by cells of the immune system.
5) plasmids are small loops of DNA that arnt part of the main circular DNA molecule. plasmids contain genes for things like antibiotic resistances and can be passed between prokaryotes. plasmids are not always present but there can be several in some cells.
6) No nucleus so the DNA floats free in the cytoplasm. its circular DNA as one long coiled up strand. its not attached to any histone proteins.
7) the flagellum is a long hair like structure that rotates to make the cell move. not every cell has one!

Question 14

what is a virus?

Answer 14

viruses are acellular so they are not cells.
viruses are just nucleic acids surrounded by protein they arnt even alive.
- they are smaller then bacteria
- they have no plasma membrane, no cytoplasm and no ribosomes.
-all viruses invade and reproduce inside the cells of other organisms. these are known as host cells.

Question 15

what are features of a virus?

Answer 15

1) contain a core of genetic material - either DNA or RNA
2) The protein coat around the core is called the capsid
3) attachment proteins stick out of the edges of the capsid. these let the virus cling onto a suitable host cell.

Question 16

what’s a transmission electron microscope?

Answer 16

• use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.
• denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
  -they give high resolution images so you can see the internal structures of the organelles like chloroplasts.
• can only be used on thin specimens

Question 17

what is a scanning electron microscope

Answer 17

• they can a beam of electrons across the specimen. this knocks of electrons from the specimen, which are gathered in a cathode ray tube to form an image
• these images you end up with show the surface of the specimen and they can be 3D
• they are good because they can be used on thick specimen
• they give lower resolution images then TEM

Question 18

how do you prepare a specimen slide? (temporary amount)

Answer 18

1. start by pipetting a small drop of water onto the slide. then use tweezers to place a thin section of your specimen on top of the water drop
2. add a drop of stain. (eosin is used to see cytoplasm, iodine in potassium iodine solution is used to stain starch grains in plant cells.)
3. then add the cover slip, next to the water droplet. then carefully tilt and lower it so it can cover the specimen. avoid air bubbles as they can obstruct your view.

Question 19

how do you use cell fractionation to separate cells?

Answer 19

(you do this in order to look at organelles separately under an electron microscope)
1) homogenisation: breaking up the cell
you can either vibrate the cell or blend it up in a blender. this breaks up the plasma membrane and releases the organelles into the solution. this solution must be kept ice cold to reduce the activity of enzymes that break down the organelles. the solution should also be isotonic which means it should have the same concentration of chemicals as the cells being broken down to prevent damage to the organelles through osmosis. a buffer solution should be added to maintain the pH.
2. filtration: getting rid of the big bits
next, the homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris, like connective tissue, from the organelles. the organelles are much smaller than the debris so they pass through the gauze.
3. ultracentrifugation: separating the organelles.
- the cell fragments are poured into a tube which is then put in a centrifuge and is spun at a low speed. the heaviest organelles like nuclei get flung to the bottom of the tube by the centrifuge. they form a thick sediment at the bottom - the pellet. the rest of the organelles stay suspended in the fluid above the sediment, the supernatant.
-the supernatant is drained off, poured into another tube, and spun in the centrifuge at a higher speed.
-this process is then repeated again at higher speeds so each time the pellet is made up of lighter organelles each time.

Question 20

what is mitosis and why does it happen?

Answer 20

mitosis is a parent cell dividing to produce two genetically identical daughter cells (they contain an exact copy of the DNA of the parent cell)
mitosis is needed for the growth of multicellular organisms and repairing damaged tissues.

Question 21

what makes up the cell cycle?

Answer 21

the cell cycle consists of a period of cell growth and DNA replication called interphase. mitosis happens after that. interphase is subdivided into three separate growth stages. These are called G1, S and G2. GAP PHASE 1 - cell grows and new organelles and proteins are made SYNTHESIS - cell replicates its DNA ready to divide by mitosis GAP PHASE 2 - cell keeps growing and proteins needed for cell division are made

Question 22

talk me through the full process of mitosis

Answer 22

4 division stages: interphase - the cell prepares to divide. the DNA is unravelled and replicated, to double its gentic content. the organelles are also replicated so it has spares ones, and its ATP content is increased (ATP provides the energy needed for cell division). 1) PROPHASE - the chromosomes condense, getting shorter and fatter. tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. the nuclear envelope breaks down and chromosomes lie free in the cytoplasm 2) METAPHASE - the chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere 3) ANAPHASE - the centromeres divide, separating each pair of sister chromatids. the spindle fibres contract, pulling chromatids to opposite poles of the spindle, centromeres first. this makes the chromatids appear V-shaped. 4) TELOPHASE - the chromatids reach the opposite poles on the spindle. they uncoil and become very long and thin again. they're now called chromosomes again. a nuclear envelope forms around each group of chromosomes, so there are now two nuclei. division of the cytoplasm (cytokines, which start in anaphase) finishes in telophase. there are now two daughter cells that are genetically identical to the original cell and to each other. mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis.

Question 23

what causes cancer/ tumours?

Answer 23

uncontrolled cell division. 1. mitosis and the cell cycle are controlled by genes. 2. Normally, when cells have divided enough times to make enough new cells, they stop. but if there's a mutation in a gene that controls cell division, the cells can grow out of control 3) the cell keeps on dividing to make more and more cells which form a tumour 4) cancer is a tumour that invades surrounding tissue

Question 24

how are cancer treatments targeting the cell cycle?

Answer 24

some cancer treatments are designed to control the rate of cell division in tumour cells by disrupting the cell cycle. this kills the tumour cells. this treatment don't distinguish cells from normal cells though - they also kill normal body cells that are dividing.

Question 25

give me the method of root tips being observed for mitosis

Answer 25

1) cut 1 cm from a growing root. it needs to be the tip because thats where growth occurs (and so thats where mitosis takes place) 2) prepare a boiling tube containing 1M hydrochloric acid and put it in a water bath at 60 degrees 3) transfer the root tips into the boiling tube and incubate for about 5 minutes 4) use a pipette to rinse the root tip well with cold water. leave the tip to dry on a paper towel 5) place the root tip on a microscope slide and cut 2mm from the very tip of it. get rid of the rest 6) use a mounted needle to break the tip open and spead the cells out thinly 7) add a few drops of stain and leave it for a few minutes. the stain will make the chromosomes easier to see under a microscope. 8) place a cover slip over the cells and push down firmly to squash the tissue. this will make the tissue thinner and allow light to pass through it. dont smear the cover slip sideways (or you will damage the chromosomes) 9) now you can look at all the stages of mitosis under an optical microscope.

Question 26

how do you observe cells using optical microscopes?

Answer 26

1) clip the slide you've prepared onto the stage 2) select the lowest powered objective lens 3) use the coarse adjustment knob to bring the stage up to just below the objective lens 4) look down the eyepiece. use coarse adjustment knob to move the stage up and down away from the objective lens until the image is roughly in focus 5) adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide 6) if you need to see the slide with greater magnification, swap to a higher powered objective lens and refocus.

Question 27

what is the formula of the mitotic index?

Answer 27

mitotic index = number of cells with visible chromosomes / total number of cells observed

Question 28

how do you use graticule and micrometre to calculate the size of cells?

Answer 28

1) eyepiece graticule and stage micro meter (like a ruler) to measure size of cells. 2) an eyepiece graticule is fitted onto the eyepiece. its like a transparent ruler with numbers, but no units 3) the stage micrometre is placed on the stage - it is a microscope slide with an accurate scale and its used to work out the value of the divisions on the eyepiece graticule at a particular magnification 4) this means that when you take the stage micrometre away and replace it with the slide containing your tissue sample, you'll be able to measure the size of the cells

Question 29

what are artefacts and how do you prevent them from obstructing your view when using a microscope?

Answer 29

artefacts are things you can see down the microscope that arnt part of the cell or specimen that your looking at. they are usually made in preparation of your slides when squashing and staining your sample and air bubbles/ dust get trapped.

Question 30

Give me two examples of cancer drug treatments where a stage of the cell cycle is affected

Answer 30

tumour cells divide much more frequently than normal cells, so the treatments are more likely to kill tumour cells. some cell cycle targets of cancer treatments include: 1. G1 - some chemical drugs prevent the synthesis of enzymes needed for DNA replication. if these arnt produced, the cell is unable to enter the synthesis phase (S), disrupting the cell cycle and forcing the cell to kill itself. 2. S phase - radiation and some drug damage DNA. at several points in the cell cycle the DNA in the cell is checked for damage. if several damage is detected, the cell will kill itself - preventing further tumour growth

Question 31

what does the mitotic index tell you and what does high mitotic index mean in plants and humans?

Answer 31

it lets u work out how quickly the tissue is growing and if there's anything weird going on. a plant root tip is constantly growing so you'd expect a high mitotic index (lots of mitosis). in other tissue samples a high mitotic index could mean that tissue repair is taking place or that there is a cancerous growth in the tissue.