unit two 2A - cell structure and transport

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. nuclear envelope
4. Golgi apparatus
5. cytoplasm
6. mitochondrion
7. smooth endoplasmic reticulum
   8.nucleus
8. nucleolus
9. rough endoplasmic reticulum
   11.plasma (cell surface) membrane

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.