B2.1 The Building Blocks Of Cells

Question 1

What does the cell membrane do?

Answer 1

Separates the contents of the cell from its surroundings. It also controls the movement of substances, like oxygen, carbon dioxide and glucose, into an out of the cell.

Question 2

What does the cytoplasm do?

Answer 2

This is where many of the chemical reactions needed for the cell to live take place. It contains organelles.

Question 3

What is an organelle?

Answer 3

A tiny structure that carries out a specific job.

Question 4

What does the nucleus do?

Answer 4

The nucleus is an organelle which contains the DNA. The nucleus controls all the activity within the cell.

Question 5

What do the mitochondria do?

Answer 5

These are organelles which respiration occurs in. They are very tiny.

Question 6

What structures does a plant cell have that an animal cell doesn’t have?

Answer 6

Cell wall- a structure made of cellulose which keeps the shape of the plant cell
Large Vacuole- a space in the cytoplasm filled cell Sao which helps to support the cell by keeping it rigid.
Chloroplasts- organelles which contain chlorophyll, a substance which absorbs light for photosynthesis.

Question 7

How much can a light microscope magnify images?

Answer 7

1500x, meaning that we can see bacteria.

Question 8

How much can an electron microscope magnify an image?

Answer 8

2 million times, meaning that we can identify key parts of bacteria cells.

Question 9

What is the chromosomal DNA?

Answer 9

A giant loop of DNA which contains most of the bacterias genetic information.

Question 10

What is plasmid DNA?

Answer 10

Plasmid DNA come in small loops, and carries some extra genetic information.

Question 11

What are the difference between the cell walls of bacteria and of plants?

Answer 11

Bacteria have a more flexible cell wall that is not made from cellulose.

Question 12

What is the role of the flagella?

Answer 12

Flagella are found on the outside of the cell, and are used by the bacteria to move themselves along.

Question 13

What is in a cell’s nucleus?

Answer 13

Chromosomes— DNA— Genes

Question 14

What do genes have?

Answer 14

Specific instructions for one protein, each gene is for one specific protein.

Question 15

Describe the structure of DNA…

Answer 15

DNA is arranged in a double helix. The two strands of the helix are linked together by bases. These bases are: adenine and thymine, guanine and cytosine. These are known as complementary base pairs and are connected by weak hydrogen bonds. The strands are made up of sugar (connected to the bases) and phosphates.

Question 16

What was the role of Wilkins and Franklin in discovering DNA?

Answer 16

In the 1950s in London they were studying the structure of DNA using X-Rays. Franklin directed beams of the Rays at purified DNA, and used photos to see how the DNA scatters the rays. From the patterns they could see that the DNA was arrange in a double helix.

Question 17

What do Watson and Crick contribute to the discovery of DNA?

Answer 17

They were trying to build a 3D molecular model of DNA They used data from other scientists, including the work of Franklin and Wilkins. However they did not reference their work, even though Crick and Watson would’ve been unable to complete their model without the others’ work.

Question 18

What is the human genome project?

Answer 18

It was an international effort to understand the human genome, which involved 18 countries. After 13 years, it was complete and scientists knew the order of the 3 billion base pairs which made up the human genome. Everyone has at least 99.9% of their DNA in common.

Question 19

What has knowing the human genome allowed for, in terms of scientific development?

Answer 19

• improved testing a for genetic disorder, because anomalies can be detected.
• new ways of finding genes which increase the risk of developing disorder.
• gene therapy
• new ways of seeing how the human genome has changed over time- how humans have evolved.
• personalised medicine, specific to a certain genotype which is more effective and causes less damage.

Question 20

What is genetic engineering?

Answer 20

Scientists can move a gene from one organism and insert it into another. Organisms which have been genetically engineered are called genetically modified organisms (GMOs).

Question 21

How is human insulin produced by genetically modified bacteria?

Answer 21

Insulin used to be extracted from dead cows and pigs, but this wasn’t very effective. The but of DNA which produces insulin from a human, is inserted into the plasmid DNA of bacteria. Insulin can then be produced in fermenters in vast quantities cheaply. Some people are not compatible with it because of the minute differences from GM insulin and human insulin.

Question 22

What are the advantages and disadvantages of golden rice?

Answer 22

Golden rice is rice which has been genetically modified to make beta-carotene, which helps with is needed by humans to produce vitamin a. This means that people with vitamin a deficiencies are at less of a risk of developing blindness or dying because the immune system is weak. However some say that the beta-carotene in GM rice is an insufficient amount to really do anything and some say that eating GM rice might cause problems, completely unproven

Question 23

What are the advantages and disadvantages herbicide resistant plants?

Answer 23

Scientists have added genes to plants to make them herbicide resistant. This reduces the amount of crop spraying farmers need to do, because they can do it all at once, making it more efficient. This process has disadvantages because cross pollination might lead to the weeds becoming herbicide resistant. This also lessens biodiversity because some organisms depend on the weeds for existence.

Question 24

What is mitosis?

Answer 24

Mitosis is the division of a diploid cell into two identical daughter cells. This is important for growth or cell repair. It begins with DNA replication, and then the copies separate.

Question 25

What is meiosis?

Answer 25

Meiosis is when a cell divides into four haploid gametes for sexual reproduction. In this,Meath chromosome is replicated and then split apart into a different cell, meaning that there are four genetically different cells.

Question 26

What is asexual reproduction?

Answer 26

Baxter reproduce asexually, where the split into two using mitosis. Some plants do this too.

Question 27

How does sexual reproduction occur?

Answer 27

In sexual reproduction, two haploid gametes combine to form a diploid zygote, when they fuse together.

Question 28

Is clinging asexual or sexual reproduction?

Answer 28

Asexual reproduction- clones are identical to their parent.

Question 29

What happens in a light microscope?

Answer 29

The light passes through the specimen and then through a magnifying lenses, making the object appear much bigger than it actually is.

Question 30

What are the stages of cloning?

Answer 30

• Removal of diploid nucleus from a body cell
• Enucleation of egg cell
• Insertion of diploid nucleus into the enucleated cell
• Stimulation of zygote with an electric shock, causing mitosis
• Implantation into surrogate

Question 31

What are human embryos cloned?

Answer 31

Because they are made up of embryonic stem cells which can differentiate into almost any type in f body cell.

Question 32

How does a stem cell become specialised?

Answer 32

When a stem cell divides, it can produce more stem cells or it can produce cells which are differentiated. A differentiated cell cannot turn into another type of cell.

Question 33

Why is using embryonic stem cells better than using adult stem cells?

Answer 33

Adult stem cells can only differentiate into a few types of cell, whilst embryonic stem cells can develop into almost any type of body cell.

Question 34

What are the advantages and disadvantages if cloning mammals?

Answer 34

• Few embryos produced in the cloning process develop successfully.
• Cloned animals age much more quickly.
• Cloned animals are also more likely to develop disorders and have health issues.
• It is good because it makes a genetically identical copy of an organism with advantageous characteristics.
• It also used to copy genetically engineered organisms.

Question 35

Why is extracting embryonic stem cells controversial?

Answer 35

Once the cells have been removed from the embryo, it dies.

Question 36

What are the advantages, disadvantages and risks of stem cell research?

Answer 36

Leukaemia can be treated using adult stem cells to destroy the cancerous white blood cells and produce new healthy blood cells. However, these cells can an be rejected by the body because they are too different. Embryonic stem cells are more effective because the body recognises them as their own cells. Using embryonic stem cells would allow for many more treatments, however it is controversial.

Question 37

How could we avoid using embryonic stem cells?

Answer 37

Scientists have begun to investigate ways of turning differentiated adult cells into stem cells by reprogramming them. Nonetheless more research is needed because these stem cells my be cancerous or produce the wrong type of cell.

Question 38

What are the four bases?

Answer 38

Adenine, thymine, cytosine and guanine. The order of these forms the genetic code.

Question 39

What are amino acids?

Answer 39

Amino acids are what makes up proteins. Cells use chains of bases in the DNA to create amino acid chains which form proteins.

Question 40

Describe transcription…

Answer 40

Transcription is the first stage of protein synthesis, which takes place in the nucleus. DNA is unzipped when the weak hydrogen bonds are broken between the bases. One strand is used as a template. Bases that are complementary to the chain, link toga their opposite it forming mRNA. RNA is very similar to DNA, but only has one strand and uracil replaces thymine. mRNA is small enough to move out of a cells nucleus and into the cytoplasm.

Question 41

Describe translation

Answer 41

In the cytoplasm the mRNA attaches to the ribosome. The ribosome then moves from one end of the mRNA to the other decoding the bass into groups of three, known as base triplets or codons. Each amino acid is attached to tRNA, each of which has a triplet of bases. The triplet controls which the amino acid is attached. As the ribosome moves to the next codon on the mRNA, the tRNA lines up with the codon. The tRNA releases the amino acid, which then joins onto the growing amino acid chain. The tRNA can then repeat its job. This continues until all of the mRNA is decoded. The amino acids form a chain called polypeptide.

Question 42

Is the order of amino a codes specific for each protein?

Answer 42

Yes it is, the order and number of amino acids determines the protein. This is because the order causes the chain to fold in a particular way, giving the chains a specific 3D shape.

Question 43

Compare the shape of keratin and insulin, haemoglobin and enzymes.

Answer 43

Keratin is formed from long fibrous molecules and is found in the hair and nails. It is also very strong. Whereas the others have more lobby shapes, meaning that they can move through the body easily. Each enzyme has a particular shape, so is very specific to this job.

Question 44

What is a mutation?

Answer 44

A mutation is a change in the sequence of bases in the genetic code, which can lead to a change in the amino acid chain, causing the protein to fold up in a different way and have a different shape, affecting how it works.

Question 45

Why is sickle cell anaemia a problem?

Answer 45

When not carrying oxygen, the sickle cells can stick together in long fibres, making the cells pointy and sickle shaped. This means that the blood cells cannot travel in small blood cells, which can lead to fatigue and weight loss.

Question 46

How can mutations be beneficial?

Answer 46

Bacteria can develop mutations to become resistant to antibiotics.

Question 47

What is an enzyme?

Answer 47

An enzyme is a particular group of proteins which is a biological catalyst for a specific reaction in the body.

Question 48

What do enzymes do during DNA replication?

Answer 48

During DNA replication in mitosis or meiosis, the double helix is unwound by an enzyme. A different enzyme then joins the bases up to their new complementary pairs.

Question 49

What do enzymes do during protein synthesis?

Answer 49

Each reaction t hat takes place in protein synthesis is controlled by a certain enzyme, for example the reaction that joins one amino acid to another is catalysed by an enzyme.

Question 50

What do enzymes do during digestion?

Answer 50

Food molecules are too lagged to pass through the cell membranes of the small in testing and into the blood. Different enzymes, therefore, are released to help with digestion in the mouth, stomach and small intestine, to break down food molecules so that they can be absorbed.
Microorganism sand fungi also release digestive enzymes. After the food molecules are digested they pass into the cell through its cell walls. Some of these enzymes in used detergents.

Question 51

What is a substrate?

Answer 51

The substance that is changed by an enzyme in a chemical reaction.

Question 52

What factors affect enzyme action?

Answer 52

• temperature is one factor. At temperatures above or below optimum, the enzymes do not work as well. This is because changing the temperature changes the shape of the active site, and if the temperature gets to high, the active site will denature. This is the same for pH.
• if the concentration of the substrate is increased, the speed of the reaction will increase up to a point, because once this point is reached, the enzyme cannot work any faster.

Question 53

Name some specific enzymes.

Answer 53

Carbohydrases catalyse the breakdown of carbohydrates.

Proteases catalyse the breakdown of proteins.

Question 54

Explain the active site

Answer 54

Looking at 3D shares of enzymes and their substrates you can see that the substrate fits into the active site of the enzyme. The substrate fits perfectly, and this is called the lock-and-key hypothesis.