CELL STRUCTURE

Question 1

Function of light microscope

Answer 1

produce a magnified of an object

Question 2

Difference between magnification and resolution

Answer 2

Magnification = how many times bigger an image is when compared with object
resolution = minimum distance apart 2 objects can be to be seen as separate item

Question 3

Explain how cell fractionation and ultracentrifugation can be used to separate cell components

Answer 3

-homogenisation - cell broken up in cold, buffered and isotonic solution to release organelles . COLD = reduce enzyme activity to prevent damage to organelles. BUFFERED - maintains constant pH to avoid damage to enzymes in organelles
ISOTONIC - same water potential as the cells, to avoid organelles from bursting/shrinking due to osmotic entry of water
-homogenate filtered to remove complete cells and large pieces of debris so it doesn’t sink to the bottom
-ultracentrifugation- spin filtrate from homogenisation at slow speed in centrifuge, heavy organelles (nuclei) fall to bottom and fluid from the top (supernatant) removed leaving nuclei as a pellet
-spin supernatant at a higher speed, next heaviest organelles (mitochondria) fall to the bottom
-repeat, spin supernatant at a even higher speed, next heaviest organelle falls to the bottom etc

Question 4

What is the function of the golgi apparatus?

Answer 4

modify and package proteins and other substances

Question 5

What is the function o fthe rough endoplasmic reticulum?

Answer 5

synthesise and transport proteins

Question 6

What is the function of the smooth endoplasmic reticulum?

Answer 6

synthesise lipids

Question 7

What is the function of the centrioles?

Answer 7

produce spindle fibres during nuclear division

Question 8

What is the function of the lysosome?

Answer 8

hydrolyse cell ‘waste’

Question 9

Describe the structure of a mitochondrion

Answer 9

double membrane, inner membrane has projections called cristae, matrix int he middle

Question 10

Describe what a complex multicellular organism is

Answer 10

Organism containing many cells with different functions

Question 11

Describe what a specialised cell is.

Answer 11

Cell with specific features to preform its role

Question 12

Give examples of 3 specialised plant cells, their functions and their adaptations to their function.

Answer 12

“Palisade cell - photosynthesis - many chloroplasts
Root hair cell - absorb water and minerals - finger like projection for large surface area
Xylem - transport water and minerals - walls contain lignin to withstand water pressure”

Question 13

Give examples of 3 specialised animal cells, their functions and their adaptations to their function.

Answer 13

“Sperm cell - male gamete - flagellum for movement, enzymes to penetrate egg
Nerve cell - transmit electrical impulses - insulating layer for rapid conduction
Muscle cell - movement - contains proteins that together can contract and shorten”

Question 14

Describe the relationship between specialised cells, tissues, organs and organ systems.

Answer 14

“Tissue: made from a group of specialised cells organised into a structureal unit performing a specific function
Organ: made from tissues working together to perform a specific function
Organ system: group of organs together performing a specific function”

Question 15

Define a prokaryotic cell.

Answer 15

Cells of organisms that do not have a nucleus or membrane bound organelles

Question 16

Define a virus.

Answer 16

Acellular, non living particle

Question 17

Describe the structure of a prokaryotic cell.

Answer 17

“Cell wall made from murein
Slime capsule surrounding the wall
Cell surface membrane
Ribosomes
Circular strand of DNA not contained in a nucleus
Plasmids - small circular pieces of DNA”

Question 18

Describe the structure of a virus.

Answer 18

“DNA or RNA enclosed within a protein coat called a capsid
Some also have a lipid envolope
Attachment proteins ont he outside”

Question 19

Compare the structure of prokaryotic and eukaryotic cells

Answer 19

“Nucleus - prokaryote non, eukaryote present, with nuclear envolope
DNA - prokaryote not associated with proteins, eularyote associcated with histone proteins
Plasmids - prokaryotes present, eukayotes absent
Membrane bound organelles - prokaryotes absent, eukaryotes present
Chloroplasts - prokaryotes absent (some do have chlorophyll), eukaryotes present
Ribosomes - prokaryotes 70s (smaller), eukaryotes 80s (larger)
Cell wall - prokaryotes present, made of murien, eukaryotes plant cells only made of cellulose
Mucliaginous capsule - prokaryotes present, eukaryotes absent”

Question 20

Describe and explain the limitations of the light microscope

Answer 20

“Poor resolution due to long wavelength of light
Often lower magnification”

Question 21

Describe the function of the scanning electron microscope

Answer 21

Beam of electrons directed on to surface of specimen from above, and scattering of electrons results in 3D image

Question 22

Describe and explain the limitations of the scanning electron microscope

Answer 22

“Requires a vacuum to avoid scattering electrons so specimen must be dead
Image may contain artefacts (objects on image that may not be on speciment) due to specimen preparation
Complex staining process
Lower resolution than TEM but much greater than light microscope”

Question 23

Describe the function of the transmission electron microscope

Answer 23

Beam of electrons focused on specimen by condenser electromagnet, beam passes through thin section of specimen, Some electrons absorbed ( dark on image), some pass through (bright on image), image produced on a screen

Question 24

Describe and explain the limitations of the transmission electron microscope

Answer 24

“Requires a vacuum to avoid scattering electrons so specimen must be dead
Image may contain artefacts (objects on image that may not be on speciment) due to specimen preparation
Complex staining process
Specimen must be extremely thin”

Question 25

Describe what mitosis is.

Answer 25

“Nuclear division of cells that produces two genetically identical daughter cells

Question 26

State when DNA replication takes place.

Answer 26

DNA replication occurs during the synthesis stage of the cell cycle

Question 27

Describe the stages of mitosis

Answer 27

“PROPHASE: 1. Chromatin condenses (shortens and thickens) to form chromosomes (becomes visible)
2. Nucleolus disappears
3. Nuclear envelope disappears
4. Centrioles to poles of cell
5. Spindles produced by centrioles
METAPHASE: 1. Spindle fibres attach to centromeres
2. Chromosomes line up on equator of cell
ANAPHASE: 1. Chromosomes pulled apart at the centromere by spindle fibres
2. Chromosomes move to the poles of the cell (evidence v shape)
TELOPHASE: 1. Chromosomes detach from spindle fibres
2. Spindle fibres disappear
3. Chromosomes uncoil and become chromatin
4. Nucleolus reappears/reforms
5. Nuclear envelope reappears/reforms”

Question 28

Explain the importance of mitosis

Answer 28

Important for growth of organisms, repair of damaged tissue, asexual reproduction in some organisms

Question 29

Describe the three stages of the cell cycle.

Answer 29

“Interphase: most of the cell cycle - DNA and organelles replicate
Nuclear division - nucleus divides into two (mitosis) or four (meiosis)
Cytokinesis - division of cytoplasm to produce two (mitosis) or four (meiosis) cells”

Question 30

Describe what happens during interphase

Answer 30

Cell grows, replicates organelles, replicates DNA, checks DNA

Question 31

Explain how mitosis is controlled

Answer 31

MItosis is controlled by two types of genes that either speed up or slow down cell division

Question 32

Describe how cancer and its treatment relate to the cell cycle

Answer 32

Caner occurs when the genes regulating mitosis and the cell cycle are damaged. The process is no longer controlled effectively leading to uncontrolled cell division and the formation of a tumour. Cancer treatments are often focused on disrupting the cell cycle.