topic 2 - cells

Question 1

name the organelles in eukaryotic cells

Answer 1

-nucleus
-cell membrane
-rough endoplasmic reticulum
-smooth endoplasmic reticulum
-golgi apparatus
-mitochondria
-ribosomes
-lysosomes
-cell wall
-permanent vacuole
-chloroplasts

Question 2

Explain the structure and function of the nucleus

Answer 2

Contains genetic material and controls cell activity

-Nuclear envelope - double membrane that controls material entry/exit

-Nuclear pores

-Nucleoplasm

-Chromosomes - protein- bound. linear DNA

-Nucleolus - smaller sphere inside - site of rRNA production and makes ribosomes

Question 3

Explain the structure and function of the endoplasmic reticulum

Answer 3

2 types of endoplasmic reticulum - system of folded membranes throughout the cytoplasm. Continuous with the outer nuclear membrane

-Rough endoplasmic reticulum - ribosomes on surface. Important in protein synthesis. Pathway to transfer proteins out of the cell

-Smooth endoplasmic reticulum - has no ribosomes. Synthesises and stores lipids and carbohydrates.

Question 4

Explain the structure and function of the Golgi Apparatus

Answer 4

-Structure similar to smooth endoplasmic reticulum just more compact
-Folded membranes form cisternae
-Secretary vesicles pinch off from the cisternae

-Add carbs to proteins to form glycoproteins
-Produce secretory enzymes
-Secrete carbs
-Transport, modify and store lipids
-Form lysosomes
-Finished products transported to cell surface in vesicles where they fuse with the membrane and the content is released.

Question 5

Explain the structure and function of lysosomes

Answer 5

-Collection of digestive enzymes

-Hydrolyse phagocytic cells
-Break down dead cells
-Digest worn out organelles for reuse of materials
-Release enzymes to outside of cell to destroy material

Question 6

Explain the structure and function of mitochondrion

Answer 6

-Site of aerobic respiration and ATP production

-Contains DNA to code for enzymes needed in respiration
-Double membrane
-Inner membrane called the cristae which increases surface area for enzymes
-Fluid centre called the mitochondrial matrix

Question 7

Explain the structure and function of ribosomes

Answer 7

Site of protein synthesis

-Small, made up of 2 sub-units containing protein and rRNA
-2 types of ribosome

-80S - large ribosome found in eukaryotic cells

-70S - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts

Question 8

Explain the structure and function of the vacuole

Answer 8

Supports the cell by making it turgid

-filled with fluid surrounded by a single membrane called a tonoplast
-Temporary store of sugars and amino acids

Question 9

Explain and structure and function of chloroplasts

Answer 9

Site of photosynthesis

-Surrounded by a double membrane
-Contains thylakoids (folded membranes embedded with pigment)
-Stack of thylakoids is called a granum
=Fluid-filled stroma - contains enzymes for photosynthesis
-Found in plants

Question 10

Explain the structure and function of the plasma membrane

Answer 10

-Controls exit/entrance of molecules

-Found in all cells
-Phospholipid bilayer

Question 11

What are the 3 types of microscopes?

Answer 11

optical, transmission electron, and scanning electron

Question 12

What is magnification?

Answer 12

How many times larger the image is compared to the actual object

Question 13

What is resolution?

Answer 13

The minimum distance between 2 objects in which they can still be viewed as separate. The resolution in an optical microscope is determined by the wavelength of light, and the resolution in electron microscopes is determined by the wavelength of the beam of electrons

Question 14

Explain the features of an optical microscope

Answer 14

A beam of light is condensed to create the image
Poorer resolution due to light having a longer wavelength
Lower magnification
Colour images
Can view living samples

Question 15

Explain the features of electron microscopes

Answer 15

A beam of electrons is condensed to create the image. Electromagnets are used to condense the beam
Higher resolving power as electrons have a short wavelength
Higher magnification
Black and white images
Sample must be in a vacuum, and therefore non-living

Question 16

How do transmission electron microscopes work?

Answer 16

Extremely thin specimens are stained and placed in a vacuum . An electron gun produces a beam of electrons that pass through the specimen. Some parts absorb the electrons and appear dark. The image is produced in 2D and shows detailed images on the internal structure of cells

Question 17

How do scanning electron microscopes work?

Answer 17

The specimens do not need to be thin, as the electrons are not transmitting through. Instead, the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours. This produces a 3D image

Question 18

What is the formula for magnification?

Answer 18

magnification = image size/actual size

Question 19

How do you calibrate the eyepiece in optical microscopes?

Answer 19

Step 1- Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece

Step 2- Count how many divisions on the eyepiece graticule fit into 1 division on the micrometer scale

Step 3- Each division on the micrometer is 10 micrometers so this can be used to calculate what one division on the eyepiece graticule is at that current magnification

Question 20

What is cell fractionation?

Answer 20

Used to isolate different organelles so they can be studied. This enables individual organelle structures and functions to be studied. The cells must be prepared in a cold, isotonic, and buffered solution

Question 21

Explain when cells are being fractionated they must be prepared in a cold, isotonic and buffered solution.

Answer 21

Cold- to reduce enzyme activity - reduces damage to organelles
Isotonic - must be the same water potential to prevent osmosis as this could cause organelles to shrivel or burst
Buffered- the solution has a maintained pH to prevent damage to organelles

Question 22

What are the 2 steps to cell fractionation?

Answer 22

Homogenisation - The cell must be broken down using a blender.Blended in a cold, isotonic and buffered solution. This solution is filtered to remove large cell debris

Ultracentrifugation - The filter is spun at different speeds in a centrifuge.
Organelles separate according to their densities

Question 23

Explain differential centrifugation

Answer 23

The centrifuge spins and the centrifugal forces cause pellets of the most dense organelles to form at the bottom

The centrifuge is first spun at a low speed and the process is repeated at increasingly faster speeds

Each time the supernatant (liquid) is removed, leaving behind a pellet of organelles

The supernatant is then spun again to remove the next pellet of organelles

Question 24

What is diffusion?

Answer 24

The net movement of particles from an area of higher concentration to an area of lower concentration

In CSM particles that pass through must be lipid-soluble

Passive process - requires no input of energy in the form of ATP

Question 25

What is facilitated diffusion?

Answer 25

Passive process but differs from simple diffusion as proteins are used to transport molecules

The movement of ions and polar molecules, which cannot simply diffuse, can be transported across membranes using protein channels and carrier proteins

Question 26

What are carrier proteins and protein channels?

Answer 26

Carrier proteins - take substances from one side of the membrane to the other
Often done by co-transport e.g. when the ion potassium is transported along the main substance glucose

Protein channels - protein pores that open or close to control the passage of selective ions e.g. potassium , sodium

Question 27

What is osmosis?

Answer 27

The movement of water particles from an area of higher water potential to an area of lower water potential across a partially permeable membrane

Question 28

What is water potential?

Answer 28

A measure of how easily water can move

When many water molecules are present they can move easier and so the higher the water potential

Measured in kilopascals (kPa)

Question 29

What is active transport?

Answer 29

The movement of molecules and ions from an area of lower concentration to an area of higher concentration using ATP and carrier proteins.

The carrier proteins act as pumps to move substances across the membrane

Very selective as only certain molecules can bind to the carrier proteins to be pumped

ATP binds to the protein on the inside of the protein and is hydrolysed into ADP and Pi. This causes the protein to then change shape and open towards the inside of the membrane, releasing the contents

when the Pi molecule is released, the protein reverts back to its original shape

Question 30

Name and explain the functions of organelles in prokaryotic cells

Answer 30

Free DNA that possesses the genetic info for the replication of bacterial cells
Plasmids - small circular DNA strands
Cell wall- physical barrier against certain substances
Capsule - protects bacterium from other cells
Flagellum - to move
Mesosome - site of respiration

Question 31

Explain the function of extrinsic and intrinsic proteins in cell surface membranes

Answer 31

Extrinsic - on the surface or only partially embedded in membrane. Give mechanical support to cell/ act as cell receptors for molecules such as hormones

Intrinsic - completely span the membrane and act as carriers to transport water-soluble materials across the membrane

Question 32

What is mitosis and what is it used for?

Answer 32

A parent cell divides to produce 2 genetically identical daughter cells
Needed for growth of multicellular organisms and for repairing damaged tissues

Question 33

Describe the cell cycle

Answer 33

Mitosis - cycle starts and ends here
G1 - Gap phase 1 - cell grows and new organelles and proteins are made
S- Synthesis - cell replicates all DNA, ready to divide by mitosis
G2 - Gap phase 2 - cell keeps growing, and proteins needed for cell division are made

Question 34

Describe the stages of mitosis

Answer 34

1 - Interphase - cell grows and DNA replicates, chromosomes not yet formed (DNA in the form of chromatin) NOT apart of mitosis

2- Prophase - chromatin condenses to form chromosomes. Centrioles move to opposite ends of cell, nuclear envelope breaks down

3- Metaphase - chromosomes align along equator of cell
-Spindle fibres connect centrioles to chromosomes by their centromeres

4- Anaphase - centromeres split, allowing chromatids to split. Nuclear envelope reforms, now 2 nuclei.

5- Cytokinesis - cytoplasm divides, 2 daughter cells have now formed

Question 35

What is an antigen?

Answer 35

Foreign proteins present on the cell surface membrane that stimulate an immune response.

Question 36

Explain phagocytosis

Answer 36

A phagocyte is a type of white blood cell
a phagocyte recognises the foreign antigens on a pathogen
the cytoplasm of the phagocyte moves around the pathogen, engulfing it
the pathogen is now contained in a phagocytic vacuole
a lysosome fuses with the phagocytic vacuole and uses its lysozymes to break down the pathogen
the phagocyte then presents the pathogen’s antigens on its surface, becoming an antigen-presenting cell
this activates other immune system cells

Question 37

What are T-cells?

Answer 37

T-cells are another type of white blood cell/
they have receptor proteins on their surface that bind to complementary antigens presented to them by phagocytes - this activates the T-cell.
Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells which kill abnormal and foreign cells
T-cells also activate B-cells

Question 38

What are B-cells? What are plasma cells?

Answer 38

B-cells are also a type of white blood cell
They are covered with antibodies that bind to antigens to form an antigen-antibody complex. This activates the B-cell to divide into plasma cells

Plasma cells are clones of B-cells
They secrete loads of antibodies specific to the antigen
An antibody has 2 binding sites so can bind to 2 pathogens at the same time. this means pathogens can become clumped together (agglutination). Phagocytes then bind to the antibodies and phagocytose as many pathogens at once