Cells

Question 1

What are exergonic reaction reactions? Examples?

Answer 1

A reaction that is accompanied by a release of energy. Products have less energy than the reactants.
Energy is trapped in the chemical bonds, so when the bonds break the energy is released
catabolic pathway
e.g respiration

Question 2

How do heterotrophs obtain nutrients?

Answer 2

Heterotrophs are dependent on autotrophs for their survival. Obtain nutrients by consuming autotrophs.

Question 3

Role of hormones in cell division

Answer 3

Hormones regulate cell division

They ensure plant growth is carefully coordinated and that the roots of plants do not grow longer than needed

Question 4

What is anaerobic respiration? Equations

Answer 4

Is the alternative form of respiration opposed to aerobic resp. Occurs in the absence of o2 and in the cytoplasm of the cell. 
Releases only 2 ATP 
Yeast 
C6H12O6-2C2H5OH + 2CO2
Animals 
C6H12O6-2C3H6C3

Question 5

What is aerobic respiration?

Answer 5

Breakdown of glucose to release energy that can be used by the cell for reactions.
Occurs in the presence of O2, in the cytoplasm of prokaryotes, and in the mitochondria in eukaryotic animals.
C6H12O6 + 6O2 - 6CO2 + 6H2O

Question 6

What is endergonic reactions?

Answer 6

Involves the absorption of energy.
Products have more energy than the reactants.
Anabolic pathway
E.g photosynthesis

Question 7

What are the principles of the cell theory?

Answer 7

1. All cells arise from pre-existing cells or the products of cells
2. Cells are the basic and simplest building blocks of life
3. All cells contain hereditary information
4. All All living organisms are made up of cells or the products of cells

Question 8

What is the purpose of meiosis?

Answer 8

Purpose is to half the chromosome number to enable greater variation among individuals. Being genetically variable increases the survival chances of organisms in changing environmental conditions.

Question 9

What are growth factors?

Answer 9

They are the hormones that regulate cell division. If they are not present then the cell will not divide.

Question 10

How do growth factors work?

Answer 10

Growth factors bind to membrane receptors on the target cell due to being complementary. Once binded it sends a relay of signals, that activates/allows the synthesis of the cyclin protein that is responsible for regulating cell division.

Question 11

What is random fertilisation?

Answer 11

Is the process when there is a random chance that a sperm will fertilise an egg. It is important as it increases the genetic variation of the zygote. Also important as it restores the diploid number.

Question 12

Differences between mitosis and meiosis?

Answer 12

The way the chromosomes are alined are different in metaphase 1. During metaphase 1, homologous chromosomes pair up side by side, whereas in mitosis they line up along the equator.
This allows the chromosome number to half.
In metaphase 2 however, the chromosomes aline like they do in mitosis.

Question 13

Why do cells from elderly people not respond to growth factors as efficiently?

Answer 13

As cell membrane could be compromised in some way that prevents growth hormones from reaching the nucleus of dividing cell. This could have occurred due to mutations, changing shape of membrane receptors, preventing the hormones from binding.

Question 14

Semi conservative replication process

Answer 14

The helicase unzips the double stranded DNA, breaking the hydrogen bonds and exposing free nucleotides on the template strand of DNA. The DNA polymerase enzyme then attaches free nucleotides to their complementary base pairs on the template strand (A-T and C-G). This results in one new strand and one old strand of DNA, hence why it is called semi-conservative.

Question 15

Process of photosynthesis

Answer 15

The light energy splits the h2o into h2 and o2. This process is dependent on light and occurs in the thylakoid of the plant cell. In the calvin cycle, the h2 then combines with the co2 to form carbohydrates such as glucose. The o2 is expelled as waste. This process does not require light and occurs in the cytoplasm/stroma of the cell. Glucose can be used as energy for the cell. and hence process converts light energy to chemical energy.
6CO2 + 6H20 - C6H12O6 + 6O2

Question 16

What is the role of the cytoskeleton? What is its basic structure?

Answer 16

The cyto has a dynamic structure, it allows protei molecules (e.g actin and tubin) to be rapidly anchored and removed which helps the cell to change shape.
Function:
- gives the cell shape
- anchors organelles
- allows the cell to move
- strengthens the cell
- assist with the assembly of spindle fibres which pull chromosomes to opposite sides of the cell

Question 17

Function of cytoskeleton in mitosis? What processes use energy during cell division?

Answer 17

Function in mitosis
Pulls sister chromosomes to opposite poles
helps move the cell membrane in the process of cytokinesis
Energy using processes
synthesis of DNA
movement of spindle fibres
new membrane

Question 18

What are intermediate filaments (medium )?

Answer 18

They are the medium sized part of the cytoskeleton (made from fibrous proteins)
Function
anchorage of the organelles such as nucleus
strengthen cells and their tissues
Found in cells such as skin cells, that are subject to wear and tear

Question 19

What are microfilaments?

Answer 19

Made from globular protein
They are the smallest part of the cytoskeleton. They play a role in cytoplasmic streaming, cytokinesis, phagocytosis, hence involved in the intracellular movement to maintain life.

Question 20

What are microtubules?

Answer 20

They are the largest component of the cytoskeleton. They are made from the actin protein.
Function
involved in the seperation of sister chromosomes in mitosis, fluid movement
Found in flagella, cilia

Question 21

Cell cycle and checkpoints. What happens at each point?

Answer 21

Checkpoint 1 - towards the end of G1 phase
In G1 - The cell grows in size and carries out metabolic reaction, including protein synthesis and respiration.
In checkpoint 1, it checks to see if the cell is large enough to divide, and has growth factors. If there is no growth factors cell will remain at G0.
S phase - semi conservative replication
G2 - protein synthesis continues, energy is accumulated in preparation for mitosis.
Checkpoint 2 (at the end of G2), checks to see if the DNA was replicated properly, and whether the MPF levels are high. MPF formed from the cyclin protein and the CDK enzyme. After the cyclin pass checkpoint, it degrades and MPF levels decrease.
M phase - mitotic division
Checkpoint 3 - metaphase, this checkpoint ensures the MPF levels have decreased (due to the cyclin degrading) and the spindle fibres are correctly attached to the centromeres.

Question 22

Checkpoint 1 - triggers of cell division

Answer 22

1. Checks to ensure size is fully grown, SA:V has decreased, thus less efficient and hence will then divide.
   Signals from the environment (physical or chemical)
   Density dependent - closely packed and will not divide
   anchorage dependent - some cells will only divide if attached to another cell
   nutrient dependent - no glucose, no ATP then no division
   Contact inhibition - of skin is broken, then cells will divide when gap is closed

Question 23

Types of cancer Genes

Answer 23

Proto onco genes - increase cell division

Tumour-suppressor genes - decrease the rate of division

Question 24

Cancer and cell division

Answer 24

Begins with a single abnormal cell, results from abnormal metabolism and growth of cells due to change in genetic makeup. Changes are caused by mutations to genomes. Mutations interfere with genes which control and regulate division. This causes uncontrolled cell division.

Question 25

Techniques for plant cell culturing

Answer 25

1. Select healthy cells from growing tissues
2. Wash in sterilising solution to remove any contaminating microbes
3. Place on a sterile growing medium (agar), which should contain materials for growth, plant growth hormones, nutrients (glucose and minerals)
4. Incubate in stable warm light environment (photosynthesis)
5. Tissue will develop and eventually leaves and roots will begin to develop

Question 26

Techniques for animal cell culturing

Answer 26

1. Select healthy tissue growing cells and sterilise the surface of the sample
2. Seperate cells using enzymes to avoid contact inhibition
3. Place in a sterile nutrient solution (glucose for resp, hormones for division, amino acids for proteins) and incubate at temperature of 37˚C
4. At intervals remove the lid and aerate to maintain an environment where cells can continually divide.
5. Cultured cells are kept at optimal temperature and will grow for 30-40 generations

Question 27

Application and limitations for plant cell culturing

Answer 27

Applications
Can prevent species from going extinct by culturing rare/endangered species.
Create a large number of identical plants to improve consistency of plants.
Limitations
All cloned, no genetic variation, thus could be wiped out in changing environmental pressures
Reduced genetic diversity (unlikely to survive environmental changes)

Question 28

Stages of mitosis

Answer 28

Interphase -produce materials for growth and synthesis of DNA before the cell divides
Prophase - the nucleus membrane disappears and chromatin condenses into chromosomes
Metaphase - Spindle fibres attach to centromere of chromosome, pull chromosomes until they are alined on the equator.
Anaphase - Spindle fibres contract and pull a sister chromatid to opposite ends of the poles of the cells.
Telophase - chromosomes unwind and become chromatin. Nuclear membrane reforms.
Cytokinesis - cell splits into two halves, resulting in two genetically identical cells

Question 29

Stages of meiosis

Answer 29

Prophase 1 - the replicated pairs of chromosomes condense and attach to each-other in a process called synapses, forming the homologous pairs of chromosomes. (crossing over occurs here)
Metaphase 1 - Spindle fibres arrange the homologous pairs of chromosomes side by side on the equator of the cell. (Diploid to haploid) (independent assortment)
Anaphase 1 - homologous pairs of chromosomes are pulled to opposite ends of the cell (each pole has a complete haploid set)
Telophase 1 -cytokinesis takes place, resulting in 2 new cells.
Prophase 2 - the nucleus membrane disappears and chromatin condenses into chromosomes
Metaphase 2 - Spindle fibres attach to centromere of chromosome, pull chromosomes until they are alined on the equator.
Anaphase 2 - Spindle fibres contract and pull a sister chromatid to opposite ends of the poles of the cells.
Telophase 2 - chromosomes unwind and become chromatin. Nuclear membrane reforms. 4 haploid cells take place

Question 30

Common features of pro and eukaryotic cells

Answer 30

Common features

Ribosomes, cell membrane, DNA, cytoplasm

Question 31

What is facilitated diffusion?

Answer 31

Channel proteins, high to low, passive, molecules are too large or charged to move through the membrane
e.g glucose, amino acids, ions

Question 32

Evidence of endosymbiosis with mitochondria and chloroplast

Answer 32

1. Double membrane
2. Own circular, plasmid DNA, unbound
3. Divide independently
4. Own ribosomes

Question 33

When did pro and eukaryotic cells first evolve?

Answer 33

Pro - 3.5 billion years ago

Eukaryotic - 1.5 billions years ago

Question 34

What are some products of cells?

Answer 34

Enzymes, hormones, antibodies

Question 35

What does permability of the membrane depend on?

Answer 35

Molecule size, charge and lipid solubility

Question 36

Application for animal cell culturing

Answer 36

Skin graphs for burn victims
Detect genetic diseases
Could grow new brain cells for undifferentiated stem cells

Question 37

Difference between plant and animal cell

Answer 37

Large vacuole, chloroplast and cell wall

Question 38

Features of DNA in mitochondria and chloroplast

Answer 38

Circular and unbound