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Biology AQA A-Level > Topic 1b > Flashcards

Topic 1b Flashcards

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1
Q

Why is water a polar molecule?

A

The shared negative electrons are pulled towards the oxygen and so the hydrogen atom is left with a positive charge while the unshared negative electons on the oxygen gives it a negative charge.

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2
Q

List the properties of water?

A
  1. Good Solvent
  2. Important metabolite
  3. High latent heat of vaporistaion.
  4. High specific heat capacity
  5. Very cohesive.
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3
Q

Name the two reactions water is involved in?

A

Condensation and Hydrolysis

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4
Q

What is a hydrogen bond?

A

A weak bond between a slightly + charged hydrogen atom in one molecule and a slightly - charged atom in another.

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5
Q

What is a metabolite?

A

A substance involved in a metabolic reaction e.g. respiration

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6
Q

What makes water a useful solvent?

A

The fact that it is polar

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7
Q

What is a high latent heat of vaporisation?

A

It means a lot of energy is required to break the hydrogen bonds between water molecules so a lot of energy is used when it evaporates. Lots of heat is needed to convert it from a liquid to a gas.

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8
Q

Explain why water has a high specific heat capacity + what is its definition?

A

It takes a lot of energy to break the hydrogen bonds between water molecules and so the energy needed to raise the temperature of 1 gram by 1 degrees is very high.

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9
Q

Why is having a high specific heat capacity a useful property of water?

A

It can buffer changes in temperature as it doesnt experience rapid temperature chages and so provides a very stable enviroment for organsims, and helps maintain a constant internal body temperature.

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10
Q

Why is water being a solvent an important property?

A

A lot of subtances involved in biological reactions are ionic and so, due to waters polarity, ions become completely surrounded and dissolve. These substances can therefore be transported around the body.

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11
Q

Why does water have a high surface tension and why is this beneficial?

A

Water is very cohesive and so has a high surface tension when it comes into contact with air. It means seat can form droplets, which can evaporate from the skin to cool an organism down.

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12
Q

Why does water having a high latent heat of vaporisation useful for organisms?

A

They can use water loss through evaporation (sweating) to cool down without lsoing too much water. This works as when water evaporates it carries away heat energy from the surface, cooling the surface thus lowering the bodies temperature.

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13
Q

Why is it important that water is transparent?

A

It allows aquatic plants to photosynthesise and means that light

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14
Q

Why is it important that water is transparent?

A

It allows aquatic plants to photosynthesise and means that light rays can penetrate the jelly like fluid that fills the eye so light can reach the retina

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15
Q

Explain how water not easily being easily compressed is a useful property?

A

It can provide support, for example the hydrostatic skeleton of animals such as the earthworm and provides turger pressure in herbaceous plants.

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16
Q

What is an inorganic ion?

A

An ion that does not contain carbon

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17
Q

Where do inorganic ions occur?

A

Cytoplasm of cells and in bodily fluids

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18
Q

What ion’s are part of haemoglobin molecules?

A

Iron ions

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19
Q

What is the role of these ions in haemoglobin?

A

They bind with oxygen to transport around the body

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20
Q

Name the ion that is linked to PH?

A

H+/ Hydrogen ions

21
Q

Which type of ion is involved in moving glucose and amino acids across cell membranes and what is the name of this process?

A

Sodium ions/Na+ in Co-transport

22
Q

What does ATP stand for?

A

Adenosine triphosphate

23
Q

Describe the structure of a molecule of ATP?

A

A molecule of adenine, a molecule of ribose and three phosphate molecules.

24
Q

How is ATP broken down?

A

ATP is broken down by a hyrolysis reaction into ADP and Pi. A phosphate bond is broken and energy is released. The reaction is catalysed by ATP hydrolase.

25
Q

How can inorganic phosphate be used?

A

It can be used to phosphorylate another compound often making it more reactive.

26
Q

What reaction occurs between ADP and Pi and why would this take place?

A

ATP can be resynthesised in a condensation reaction between ADP and Pi, catalysed by the enzyme ATP synthase. This happens during photosynthesis and respiration.

27
Q

Why is ATP and better immediate energy source than glucose?

A
  • Each ATP molecule releases less energy than each glucose molecule and energy can therefore be released in smaller more manageable quantities.
  • The hydrolysis of ATP to ADP is a single reaction that releases immediate energy wheras the breakdown of glucose is a long series of reactions and so takes much longer.
28
Q

What energy requiring processes is ATP used for?

A

Metabolic processes- building macromolecules from basic units.
Movement- ATP provides energy for muscle contraction, so filaments of muscle slide past one another shortening the length of the muscle fibre.
Active transport- Provides energy to change the shape of plasma proteins into carrier protein, allowing molecules or ions to be moved against a concentration gradient.
Secretion- ATP is needed to to form the lysosomes needed for the secretion of cell products.
Activation of molecules- Pi can be used to phosphorylate other compounds making them more reactive thus lowering the activation energy.

29
Q

How does ATP store energy?

A

The bonds between the phosphate groups are unstable and so have a low activation energy which can easily be broken, however when they do break they release a considerable amount of energy.

30
Q

What is the function of DNA?

A

To store genetic infomation

31
Q

What are ribosomes made from?

A

Ribosomal RNA and proteins

32
Q

Describe the structure of a DNA nucleotide?

A

A phosphate group, a deoxribose sugar and a nitrogen containing organic base linked by condensation reactions.

33
Q

Name the four possible bases in DNA?

A

Adenine, Thymine, Guanine and Cytosine

34
Q

How is a polynucelotide chain formed?

A

This is many nucelotides joined together in condensation reactions between the phosphate group of one nucleotide and the pentose sugar of another forming a phophodiester bond. The chain of phosphates and sugars is caalled the sugar phosphate backbone

35
Q

Describe how the DNA helix is formed?

A

Two DNA polynucleotide strands join together by hydrogen bonding between the complementary base pairs- A with T, C with G. Three H bonds form with C and G, Two with A and T. The antiparallel strands then twist around each other to form the DNA double helix.

36
Q

Name the sugar in RNA?

A

Ribose

37
Q

Name the four bases in RNA?

A

A, T, G and Uracil

38
Q

Describe the deifferences between RNA and DNA?

A

DNA is long and double stranded wheras RNA is short and single stranded.
DNA contains deoxyribose pentose sugar, RNA has ribose.
DNA contains ATCG, wheras RNA has AUCG

39
Q

Who and when worked out the structure of DNA?

A

In 1953 James Watson and Francis Crick after following the work done by Rosalind Franklin.

40
Q

Why is DNA a stable molecule?

A

The phophodiester bonds help protect the more chemically reactive bases inside the double helix.
Hydrogen bonds link the base pairs forming bridges/rungs between the phosphodiester uprights. As C and G have 3 H bonds the higher the quantity the more stable the DNA molecule.

41
Q

How is DNA adapted to carry out it’s functions?

A
  • Very stable structure that rarely mutates.
  • Two seperate strands joined by H bonds which allow them to seperate during DNA replication and protein synthesis.
  • Large so can carry a lot of genetic infomation.
  • Base pairing means DNA replicate and transfer genetic infomation as RNA.
  • As the base pairs are within the helical cylinder the gentic infomation is protected by outside chemical and physical forces.
42
Q

Why is the process of DNA replication described as semi conservative?

A

Because half of the strands in the new DNA molecule are from the original DNA molecule, providing genetic continuity between generations of cells.

43
Q

Describe the 1st stage of replication?

A

The enzyme DNA helicase breaks the bonds between the bases on the two polynucletide strands, making the helix unwind leaving two seperate strands.

44
Q

Describe the 2nd stage of replication?

A

Each original strand of DNA acts as a template strand for a new strand. Complimentary base pairing takes place between the free floating DNA nucleotides and the exposed bases on the original template strands.

45
Q

Describe the 3rd stage of replication?

A

The enzyme DNA polymerase joins the nucletides together in condensation reactions, where hydrogen bonds are formed.

46
Q

How does DNA polymerase act on the DNA strands?

A

Each end of DNA has a different structure, one end is 3’ one end is 5’, DNA polymerase is only complimentary to the 3’ end and so enzymes can only be added to the new strand at the 3’ end. This means the new strand is formed in a 5’ to 3’ direction and DNA polymerase moves down the template strand in a 3’ to 5’ direction.

47
Q

Who theorised semi conservative replication?

A

Meselson and Stahl.

48
Q

Describe the experiment that provided eveidence for semi conservative replication?

A

Two samples of bacteria were grown, on in N14 the other in N15, as the bacteria reproduced they took up nitrogen from the broth to help make nucleotides for new DNA.
A sample of DNA was taken from both smaples and spun in a centrifuge, the DNA from N15 settles lower as it was heavier.
Then this sample was placed in a broth of N14 and later a sample was spun in the centrifuge.
The DNA settled in between where N14 and N15 settled, showing that the DNA contained both N14 and N15.

Biology AQA A-Level (18 decks)

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