2.1 eukarotes and prokaryotes

Question 1

2.1 v

state the principle of the cell theory

Answer 1

cella are fundamental structural units in all living organisms. they determine the function and organisation of biological systems.

Question 2

describe difference between organ and tissue

Answer 2

A tissue is a group of similar cells

am organ is tissues working together to perform a specific function

Question 3

what is the nucleoid

Answer 3

irregularly-shaped region of cytoplasm where loop of bacterial DNA is located

Question 4

what is a plasmid

Answer 4

1 or more rings of DNA found in some bacterial cells
contains non-essential genes(not needed for the survival of bacteria)
can be exchanged between bacterial cells via conjugation

Question 5

describe the structure of a bacterial cell wall and slime capsule

Answer 5

peptidoglycan(murein) cell wall provides mechanical strength

may be coated by slime layer to prevent desiccation(drying) ,adhere cells and provide nutrients

Question 6

outline process of gram staining

Answer 6

1. fixation-imobalises bacteria and makes it more permeable to dyes
2. crystal violet dye-absorbed by peptidoglycan
3. iodine solution forms crystals in violet dye
4. decorization- alcohol gram positive will be clear as dyes will be washed out. gram negative will stay purple as peptidoglycan has more layers
5. add red safranin to make negative appear red and examine under microscope

Question 7

describe gram positive cell walls

Answer 7

have thicker layer of pepidoglycan (insoluble in alcohol)
purple under microscope when stained

Question 8

describe gram negative cell walls

Answer 8

thinner layer of petidoglycan with outer lipopolysaccharide membrane(surface membrane) (alcohol-soluble)
appear red under microscope when stained

Question 9

why do Gram positive and Gram negative bacteria respond differently to certain antibiotics

Answer 9

Gram negative bacteria have an outer membrane and a much thinner peptidoglycan layer, they are not affected.

Question 10

compare ribosomes in eukaryotic and prokaryotic cells

Answer 10

formed of protein and rRNA
made up of a large and a small subunit. During translation, the two subunits come together around a mRNA molecule, forming a complete ribosome.

Question 11

contrast ribosomes in eukaryotic and prokaryotic cells

Answer 11

larger subunit eukaryotic: 80S (bigger)
smaller subunit prokaryotic 70S (smaller)

Question 12

describe the structure of the nucleus

Answer 12

surrounded by nuclear envelope, a semi permeable double membrane

nuclear pores allow substances to enter and exit

dense nucleolus made of RNA and proteins assembles ribosomes

Question 13

describe the function of the nucleus

Answer 13

contains DNA in chromosomes coiled around chromatin

controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis

Question 14

describe the structure and function of the endoplasmic reticulum(ER)

Answer 14

Cisternae- network of tubules and flattened sacs extends from cell membrane and connects to nuclear envelope
rough ER(has ribosomes on outside)- many ribososmes attached from protein synthesis and transport
smooth ER-lipid synthesis

Question 15

Describe the structure of a mitochondrion

Answer 15

surrounded by double membrane

folded inner membrane forms cristae: site of electron transport chain
fluid matrix-contains mitochondrial DNA,respiratory enzymes,lipids,proteins

Question 16

describe structure of chloroplast

Answer 16

vesicular plastid with double membrane
thylakoids-flattened discs stack to form grana- photosystems with chlorophyll
intergranam lamellae-tubes attach thylakoids in adjacent grana
stroma-fluid filled matrix

Question 17

state the function of mitochondria and chloroplasts

Answer 17

mitochondria- site of aerobic respiration to produce ATP
chlotoplats-site of photosynthesis to convert solar energy into chemical energy

Question 18

describe the structure and function of the Golgi apparatus

Answer 18

planar stack of membrane-bound, flattened sacs

molecules are processed in cisternae vesicles

Proteins and lipids from the ER enter the Golgi apparatus at its cis face and exit at its trans face.

Exit via exocytosis(large number of molecules transferred out of the cell)

modifies and packages proteins for export

synthesises glycoproteins

Question 19

describe the structure and function of a lysosome

Answer 19

structure
bag of digestive enzymes

function
phagaocytosis in white blood cells
first the white blood cell forms a vacuole around the bacteria this is called a phagasome; the lysosome fuses with the phagasome and lysosomal enzymes digests the bacteria the soluble digestion products now pass into the cytoplasm

exocytosis-release enzymes outside of the cell to destroy material

digest worn-out organelles for the reuse of materials

Question 20

structure and function plant cell wall

Answer 20

made of cellulose microfibrils for mechanical strength

plasmodesmata connect the two cytoplasms together- these connections form the symplast and the symplastic pathway pathway- to allow molecules to pass between cells through cytoplasm

cell walls join for the appoplast and the appoplastic pathway- material are able to move through the cell wall

middle lamella separates adjacent cell walls (like the glue)
hemicelluloses harden the walls further.
Pectin-(polysaccharide) found in fruits, helps bind cells together

Question 21

describe the structure of the cell vacuole in plants

Answer 21

filled with fluid surrounded by a single membrane called tonoplast

stores cell sap, which contains mineral ions,water, enzymes, soluble pigments

Question 22

describe the function of the cell vacuole in plants

Answer 22

controls turgor pressure
absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

Question 23

describe the structure and function of animal vacuoles

Answer 23

numerous and much smaller than in plants
temporary membrane bound sacs containing water and chemicals
more commonly referred to as vesicles

Question 24

describe the structure and function of centrioles

Answer 24

spherical group of 9 microtubules arranged in triplets

located in centrosomes

migrate to opposite poles of cell during prophase and spindle fibres form between them

Question 25

What is Cell fractionation

Answer 25

A process which allows scientists to extract pure samples of a particular organelles eg mitochondria

Question 26

Steps of cell fractionation

Answer 26

1) The tissue for example liver is chopped up. When cells are broken apart substances mix together and begin to react
2) to prevent this a fluid is added that is
Ice cold- minimise enzyme reaction
Isotonic- same water concentration so cells don’t burst
Contains a buffer- to resist any changes in pH
3) the mixture is put in a homogeniser(blender) to break up the cells
4) the resulting mixture is centrifuged at high speeds(mixed) this separates the organelles depending on their density and shape. The densest organelles to sediment out are the nuclei. The remaining fluid is supernatant which poured off and centrifuged again to collect other organelles

The order of sedimentation and density is:
1) nuclei
2) mitochondria
3) rough ER
4) smooth ER
5) ribosomes