Cells as the basis of life

Question 1

What are the 3 key statements in The Cell Theory?

Answer 1

All cells come from pre-existing cells

All living things are made out of cells or products of cells

Cells are the smallest independent unit of life

Question 2

Give an example of:
* A prokaryotic organism
* A single celled eukaryotic organism
* A multicellular eukaryotic organism

Answer 2

• A prokaryotic organism
  Bacteria
• A single celled eukaryotic organism
  Protists
• A multicellular eukaryotic organism
  Plantae

Question 3

List the common features of a eukaryotic and prokaryotic cells

Answer 3

Cell membrane
Ribosome
Cytoplasm
DNA

Question 4

Compare prokaryotic and eukaryotic cells

size:

internal organisation:

shape and location of chromosomes:

Answer 4

Size:
prokaryote = smaller
eukaryote = larger

Internal organisation:
prokaryote = simple, no membrane-bound organelles
eukaryote = complex many membrane-bound organelles

Shape and location of chromosomes:
prokaryote = circular DNA, in cytoplasm
eukaryote = DNA arranged in linear chromosomes, in nucleus

Question 5

State the function of Nucleus

Answer 5

Contains the genetic information of the cell (DNA in the form of chromosomes)

Question 6

State the function of Nucleolus

Answer 6

Responsible for the production of ribosomes

Question 7

State the function of mitochondrion

Answer 7

Site of aerobic respiration

Question 8

Explain two features of the chloroplast that allow it to perform its function.

Answer 8

Function: site of photosynthesis

Contains chlorophyll
Has internal membranes that are highly folded
This increases their surface area
This allows a greater number of enzymes to be embedded in the membranes
This allows a greater rate of photosynthesis due to more reactions being able to take place at any given time
(more active sites available)
More enzymes and chlorophyll facilitate photosynthesis
This increases the efficiency of photosynthesis

Question 9

state the function of vacuole

Answer 9

Storage of materials such as nutrients, water, and solutes

Question 10

state the function of vesicle

Answer 10

Transportation of materials

e.g., newly synthesised proteins

Question 11

state the functionm of golgi body

Answer 11

modification and packaging of cell products

e.g., proteins

Question 12

state the function of Rough endoplasmic reticulum (RER)

Answer 12

site of protein synthesis and transportation

Question 13

state the function of of smooth endoplasmic reticulum

Answer 13

synthesis and transport of lipids

Question 14

state the function of ribosome

Answer 14

Protein synthesis from animo acid

Question 15

state the function of cytoskeleton

Answer 15

Facilitate the movement of organelles into correct orientation, maintain the shape of cell

Question 16

state the function of lysosome

Answer 16

Digestion and breakdown of excess worn out organelles and engulfed bacteria and viruses

Question 17

Describe the fluid mosaic model

Answer 17

Fluid – flexible, allows the movement of molecules in and out of the cell

Mosaic – contains embedded proteins and other molecules pieced together like a mosaic

Question 18

state the function of the cell membrane

Answer 18

To control the movement of molecules (materials, nutrients, and wastes) between the cell and its environment

Question 19

Why do phospholipids arrange themselves into a bilayer?

Answer 19

Due to their chemical nature

Arranged so the hydrophilic heads face outwards, and hydrophobic tails turn inwards facing each other

Question 20

• Give examples of types of proteins found in a cell membrane

Answer 20

Enzymes
Receptor proteins
Carrier proteins
Protein pumps
Protein channels

Question 21

Describe the process of exocytosis

Answer 21

1. Golgi body packages material into vesicle
2. Vesicle moves to the cell membrane and fuse with it
3. Vesicle open outwards and expels the content into the external environment
   (movement of the cell membrane and vesicles is facilitated by the cytoskeleton)

EX. releasing of hormones into blood stream

Question 22

Describe the process of endocytosis

Answer 22

1. Cell membrane surround and engulf molecules then fuse with it to form a vesicle and draw the molecules inside the cell
   (movement of the cell membrane and vesicles is facilitated by the cytoskeleton)

EX. single celled cells obtaining food

Question 23

Describe the process of crossing over and explain why it is important

Answer 23

Crossing over is the exchange of genetic material between the non-identical sister chromatids on different homologous pair of chromosomes

This creates new combinations of maternal and paternal alleles
It is important as it increases the chances of genetic variation which increases the chances of a population’s survival

Question 24

Describe independent assortment, stating what 2 stages of meiosis it occurs in

Answer 24

• anaphase 1 & 2
• The arrangement of homologous pair of chromosomes is random
• Each of the homologous pair of chromosomes is arranged independently from the other pair
• This greatly contributes to genetic variation by increasing the number of possible combinations of genes in the gamete cells

Question 25

Explain how mutations caused by carcinogens can upset normal controls of cell division.

Answer 25

- Carcinogens increase the chances of a mutation occurring - A mutation causes a change in the gene that codes for a cell cycle regulator - This leads to changes in the shape and function of the regulator - This may lead to failure to stop a cell at a checkpoint or may lead to a damaged cell to pass through a checkpoint

Question 26

Explain how hormones and other proteins (CDK/Cyclin) may regulate the cell cycle and cell division.

Answer 26

Growth factors are types of hormones that regulate the cell cycle Growth factors stimulate the cycle cell - Hormones bind to the membrane receptors and signal the cell to alter the levels of proteins produced - The level of proteins such as CDK and cyclin synthesised control whether a cell can go pass a checkpoint or not - - CDK are enzymes - Cyclins bind to CDK to active them, the activated CDK acts as a signal to turn on certain processes

Question 27

Name the 3 things the G1 checkpoint checks for.

Answer 27

- Check for cell size - Check for nutrients - Check for growth factors

Question 28

State the 2 things the G2 checkpoint checks for.

Answer 28

- Check for correct DNA replication - Check for DNA damage

Question 29

What does the metaphase checkpoint check for?

Answer 29

- Check for correct spindle attachment

Question 30

Describe the stages in the cell cycle: G1 – Growth 1 S phase (DNA synthesis G2 – Growth 2 M phase – Mitosis

Answer 30

G1 – Growth 1 - Cell physically grows larger and makes the molecular building blocks required in later steps S phase (DNA synthesis - cell synthesising a complete copy of the DNA in the nucleus via DNA replication G2 – Growth 2 - creates proteins and copies organelles - reorganise the content in preparation for mitosis - cells grows more M phase – Mitosis - prophase, metaphase, anaphase, telophase, cytokinesis

Question 31

Describe and represent (draw) Binary fission in prokaryotic cells

Answer 31

1. Bacterial DNA replication 2. Each of the two copies of the circular DNA attaches to cell membrane 3. Cell grows and in doing so the DNA moves from each other 4. The cell membrane folds inwards to divide the cell into 2 (cytokinesis) 5. 2 daughter cells produced, which are identical to each other and parent cell (have identical circular

Question 32

State the two processes within the cell cycle that ensure the production of genetically identical daughter

Answer 32

- DNA replication - separation of identical sister chromatids

Question 33

Explain why the amount of DNA in a cell doubles before cell division

Answer 33

To make sure each daughter cell contains identical copy of the genetic material in its chromosomes and to be fully functional This occurs during DNA replication

Question 34

Cells may divide for? 4 things

Answer 34

- repair - growth - replacement - reproduction

Question 35

Explain why a different enzyme is needed to catalyse each step in a metabolic pathway.

Answer 35

- Enzymes are specific to substrates due to complementary shapes - Enzyme has an active site that is complementary in shape to one substrate - Each step has a different substrate and so requires a different enzyme

Question 36

State and explain two benefits of chemical reactions occurring in small steps.

Answer 36

Avoid large changes in temperature - only small amounts of heat is released at a time - heat can be dissipated easily - this maintains stable temperature - large changes in optimal temperature would affect enzyme activity OR Efficient conversion of energy into ATP - Large releases of energy would lead to more loss of energy as heat

Question 37

What is the definition of cell metabolism?

Answer 37

- The total of the catabolic and anabolic reactions occurring in a cell - Is critical to the survival of a cell

Question 38

Describe how ATP is formed state the cell activities in the form of ATP is required by cells for

Answer 38

- Metabolic reactions such as cellular respiration releases energy - This means, there is a net release of energy from the breakdown of molecules - The produced energy is used to form ATP from ADP + Pi (ATP is formed when a phosphate is added to ADP (ADP + Pi) ) - This energy is used for many cell activities such as : - Cell movement - Synthesis - Maintaining a stable environment

Question 39

Describe how energy is released from the conversion of ATP to ADP and Pi

Answer 39

- When breaking the bond in ATP to form ADP and Pi (when a phosphate is removed from ATP), there is a net release of energy - The produced energy is used for many cell functions

Question 40

State: - the word and chemical eqution of **aerobic respiration** - location - where it occurs - type of cells it occurs in

Answer 40

Glucose + oxygen --> carbon dioxide + water C6H12O6 + 6O2 ---> 6CO2 + 6H2O location: Mitochondria type of cells: plants & animals

Question 41

State: - the word and chemical eqution of **alcohol fermentation** - location - where it occurs - type of cells it occurs in

Answer 41

Glucose ---> ethanol + carbon dioxide C6H12O6 --> 2C2H5OH + 2CO2 location: cytoplasm type of cells: yeast, plants, some bacteria

Question 42

State: - the word and chemical eqution of **lactic acid fermentation** - location - where it occurs - type of cells it occurs in

Answer 42

Glucose --> lactic acid C6H12O6 ---> 2C3H6O3 location: cytoplasm type of cells: Animals

Question 43

Distinguish between autotrophs and heterotrophs

Answer 43

Autotroph: Use light energy in photosynthesis to store chemical energy in carbohydrates (glucose) e.g., Plant Heterotroph: Take in chemical energy in complex molecules produced by other organisms e.g., Animal

Question 44

Use examples to explain why different materials move through the cell membrane by different mechanisms Based on: 1. Nature of molecule (hydrophilic, hydrophobic, charged ions) 2. Size (small or large) 3. Direction (with or against concentration gradient)

Answer 44

- Small hydrophobic molecules move in and out of the cell directly through cell membrane (lipid bilayer) via simple diffusion, e.g., oxygen - Small hydrophilic or charged ions move in and out the cell through protein channels embedded in the cell membrane via facilitated diffusion e.g., glucose or calcium ions - Large molecules move in and out the cell through endocytosis and exocytosis respectively, movement of cell membrane is facilitated by the cytoskeleton e.g., exocytosis: secretion of wastes or newly synthesised proteins endocytosis: single celled cells obtaining food

Question 45

* How does surface area to volume ratio of the cell affect movement across a membrane?

Answer 45

1. Size - Small cells have increased surface area to volume ratio than large cells 2. Shape - Long and thin shaped cells have increased surface area to volume ratio - High surface increases the frequency and chances of successful collisions between particles, low volume decreases the distance travelled by particles, this increases the rate of transportation of molecules (e.g., osmosis/diffusion)

Question 46

* How does the concentration gradient affect movement across a membrane?

Answer 46

- Concentration gradient is the difference between the concentration intracellularly and extracellularly - The greater this difference, the steeper the concentration gradient - This increases the rate of the molecules’ movement