Cells

Question 1

List the 10 organelles in eukaryotic cells

Answer 1

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

Question 2

Describe the structure and function of the nucleus.

Answer 2

S:A large spherical organelle surrounded by a double membrane (nuclear envelope).
F:Site of DNA replication and transcription, contains the genetic code for each cell

Question 3

Describe the structure and function of the rough endoplasmic reticulum.

Answer 3

S:A network of flattened sacs studded with ribosomes, attached to nucleus
F:Protein synthesis

Question 4

Describe the structure and function of the smooth endoplasmic reticulum.

Answer 4

S:A network of flattened sacs, no ribosomes, not attached to nucleus
F:Synthesis of and store lipids and carbohydrates

Question 5

Describe the structure and function of the golgi apparatus and golgi vesicles.

Answer 5

S:Folded membranes making cisternae, vesicles are pinched off sacs of golgi apparatus
F:Packages and moves around proteins and lipids in preperation for export out of the cell, produce secretory enzymes ,finished products are transported to cell surface in vesicles where they fuse with membrane + releases contents

Question 6

Describe the structure and function of lysosomes.

Answer 6

S:A membrane bound organelle containing digestive enzymes known as acid hydrolases
F:Hydrolyse phagocytic cells, break down completely dead cells( AUTOLYSIS), release enzymes outside of cell to destroy material (EXOCYTOSIS), digest worn out organelles

Question 7

Describe the structure and function of mitochondria.

Answer 7

S:Smooth, capsule shaped, double membrane organelle containing an inner membrane called the cristae, fluid centre called mitochondrial matrix
F:Site of aerobic respiration, site of ATP production

Question 8

Describe the structure and function of ribosomes.

Answer 8

S:Small, made up of 2 sub-units of proteins and rRNA–
80s- large ribosome found in eukaryotes
70s- smaller ribosome found in prokaryotes, mitochondria and chloroplasts
F:Site of protein synthesis

Question 9

Describe the structure and function of chloroplasts.

Answer 9

S:Surrounded by a double membrane, contains thylakoids, fluid filled stomata contains enzymes for photosynthesis, found in plants
F:Site of photosynthesis

Question 10

Describe the structure and function of vacuole.

Answer 10

S:Filled with fluid surrounded by a single membrane called a tonoplast
F:Make cells turgid+therefore provide support, temporary store of sugars and amino acids

Question 11

Describe the structure and function of cell wall.

Answer 11

S:
Plants- made of microfibrils of the polymer cellulose
Fungi- made of chitin a nitrogen containing polysaccharide
F:Provide structural strength to cell

Question 12

Describe the structure and function of cell membranes.

Answer 12

S:Phospholipid bilayer which creates the partially permeable membrane
F:Controls entrance and exit of molecules

Question 13

What are membranes described as?

Answer 13

A fluid-mosaic model (due to mixture and movement of the phospholipids, proteins, glycoproteins, and glycolipids)

Question 14

Describe the structure of the phospholipid bi-layer.

Answer 14

The hydrophilic heads are attracted to water and therefore face outwards whereas the hydrophobic tails repel water, so they face inwards.

The head (negative charge) contains a phosphate group and a glycerol molecule. The tail contains fatty acid chains which have no charge, meaning they repel water.

Question 15

Why is cholesterol present in some membranes?

Answer 15

It restricts the lateral movement of other molecules in the membrane. This is useful as it makes the membrane less fluid at high temps + prevents water and dissolved ions leaking out of the cell.

Question 16

Why are proteins embedded across the membrane? What are the 2 types?

Answer 16

-Peripheral proteins: provide mechanical support or are connected to proteins or lipids to make glycoproteins and glycolipids
-Integral proteins: are protein carriers or channel proteins involved in the transport of molecules across the membranes

Question 17

Describe the difference between protein channels and protein carriers.

Answer 17

Channels:form pores in the membrane for charged particles to diffuse through down the conc gradient
Carriers:bind with larger molecules such as glucose and change shape to transport them to the other side of the membrane

Question 18

Describe how protein channels work.

Answer 18

THIS IS A PASSIVE PROCESS, NO ENERGY IS NEEDED AND REQUIRES A CONC GRADIENT!!
1.made from water filled hydrophilic passages
2.these allow water soluble ions to pass through
3.channels are selective: they can only open in the presence of specific ions
4.ions bind with proteins causing protein shape to change so 1 side is open and 1 is closed

Question 19

Describe how protein carriers work.

Answer 19

THIS IS A PASSIVE PROCESS, NO ENERGY IS NEEDED AND REQUIRES A CONC GRADIENT!!
1.process for big, bulky molecules
2.carrier proteins are specific and will only bind to specific molecules
3.when binded, it changes 3D tertiary structure so molecule can be released on the other side

Question 20

How do cells divide in eukaryotes, prokaryotes and viruses?

Answer 20

Eukaryotes=cells enter cell cycle and divide by mitosis or meiosis

Prokaryotes=replicate by binary fission

Viruses=no cell division b/c not living, they replicate inside of host cells they invade by injecting their nucleic acid in to replicate virus particles

Question 21

Describe the cell cycle.

Answer 21

1. Interphase; G1=growth, S=DNA replication, G2=growth and preparation
   2.Nuclear division; mitosis or meiosis
   3.Cytokinesis

Question 22

Briefly describe mitosis.

Answer 22

Interphase
4 Key stages:
-Prophase
-Metaphase
-Anaphase
-Telophase

One round of division, genetically identical cells are made, diploid cells made, purpose for growth and repair

Question 23

Describe prophase.

Answer 23

-Chromosomes condense and become visible, nucleolus disappears!!
-In animal cells, centrioles(make spindle fibres) separate and move to opposite poles of the cell

Question 24

Describe metaphase.

Answer 24

The chromosomes align along the equator of the cell, the spindle fibres released from the poles now attach to the centromere and chromatid

Question 25

Describe anaphase.

Answer 25

Chromosomes break at centromeres and sister chromatids move to opposite ends of the cell!!

REQUIRES ENERGY IN THE FORM OF ATP

Question 26

Describe telophase.

Answer 26

Chromosomes are now at each pole and become longer and thinner. Spindle fibres disintegrate and nucleus starts to reform. Final stage is when cytoplasm splits in 2 to create the 2 new genetically identical cells/

Question 27

Name the 5 key types of transport.

Answer 27

1.simple diffusion
2.fracilitated diffusion
3.active transport
4.osmosis
5.co-transport

Question 28

Describe simple diffusion.

Answer 28

‘The net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. This process doesn’t require ATP.’

Molecules must be lipid soluble and small.

Question 29

Describe facilitated diffusion.

Answer 29

This is a passive process so it doesn’t require ATP like SD, but it differs as proteins are used to transport molecules. The movement of ions and polar molecules which cannot diffuse can be transported across membranes by facilitated diffusion using protein channels and carrier proteins.

-Protein channels=form tubes filled with water which enables water soluble ions to pass through the membrane. This is selective as channels only open in presence of certain ions when they bind to the protein.
-Carrier proteins=will bind with a molecule which causes a change in shape of protein. The shape enables the molecule to be released to the other side.

Question 30

Describe osmosis.

Answer 30

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

Question 31

What is water potential?

Answer 31

The pressure created by water molecules and is measured in kPa.

Pure water=water potential of 0
So when solutes are dissolved in water, the water potential will become negative.(The more negative the water potential the more solute dissolved)

Question 32

Describe isotonic, hypertonic and hypotonic solutions.

Answer 32

-Isotonic=water potential is the same in the solution and the cell within the solution
-Hypertonic=-water potential of a solution is more negative than the cell
-Hypotonic=water potential of a solution is more positive(close to 0)than the cell.

Question 33

Describe what happens to animal cells and plant cells if they are placed in a hypotonic solution.

Answer 33

1.a lot of water will move into the cell by osmosis.
2.as animal cells don’t have a cell wall, the pressure will cause the cell to burst
3.as plant cells do have a cell wall, they instead become turgid

Question 34

Describe what happens to animal cells and plant cells if they are placed in a hypertonic solution.

Answer 34

Both animal and plant cells will shrink and become shrivelled due to large volumes of water leaving the cell by osmosis

Question 35

Describe the process of binary fission in bacterial cells.

Answer 35

1.replication of circular DNA
2.replication of plasmids
3.division of cytoplasm to produce daughter cells