Topic 3 Chemicals of Life

Question 0

3.1.2

Outside of the four main elements what other elements are needed by living organisms?

Answer 0

Sulphur
Calcium
Phosphorus
Iron
Sodium

Question 1

3.1.1

What are the most frequently occurring elements in living things?

Answer 1

Carbon (19%)
Hydrogen (10%)
Oxygen (65%)
Nitrogen (3%)

Question 2

3.1.3

What is the role of sulphur in living organisms?

Answer 2

Found in certain amino acids (cysteine and methionine), allowing proteins to form disulphide bonds

Question 3

3.1.3

What is the role of calcium in living organisms?

Answer 3

Found in bones and teeth, also involved in neurotransmitter release in synapses

Question 4

3.1.3

What is the role of phosphorus in living organisms?

Answer 4

Component of nucleic acids and cell membranes

Question 5

3.1.3

What is the role of iron in living organisms?

Answer 5

Found in haemoglobin (animals), allowing for oxygen transport

Question 6

3.1.3

What is the role of sodium in living organisms?

Answer 6

Involved in the generation of nerve impulses in neurons

Question 7

3.1.5

Outline the thermal properties of water

Answer 7

• Water has a high specific heat capacity (the measure of energy required to raise the temperature of 1g of substance by 1 degree C)
• Water has a high heat of fusion (amount of energy required to be lost to change 1g of liquid to 1g of solid at 0 degrees C)
• These properties occur as a result of the extensive hydrogen bonding between water molecules - this allows water to absorb considerable amounts of energy with little change in (H-bonds need to be broken first)

Question 8

3.1.5

Outline the cohesive properties of water

Answer 8

Water molecules are strongly cohesive
Water molecules will also tend to stick to other molecules that are charged or polar
These properties occur as a result of the polarity of water and its ability to form hydrogen bonds with appropriate molecules

Question 9

3.1.5

Outline the solvent properties of water

Answer 9

Water can dissolve many organic and inorganic substances that contain electronegative atoms
This occurs because the polar attraction of large qualities of water molecules can sufficiently weaken intramolecular forces (e.g. Ionic bonds) and result in the dissociation of the atoms

Question 10

3.1.6

Explain the relationship between the properties of water and it’s use in living organisms as a coolant.

Answer 10

Both plants and animals use the evaporation of water from the surfaces of their bodies to facilitate cooling (sweating and panting in animals, transpiration from leaves in plants)
Water can be used to carry heat to cooler places in our bodies

Question 11

3.1.6
Explain the relationship between the properties of water and it’s use in living organisms as a medium for metabolic reactions

Answer 11

Water can dissolve many substances to facilitate chemical reactions
Water can also absorb thermal energy released as a byproduct of many chemical reactions

Question 12

3.1.6

Explain the relationship between the properties of water and it’s use in living organisms as a transport medium

Answer 12

The forces of attraction between water molecules help facilitate the transport of water up the xylem of plants
Water is an effective transport of medium for dissolved substances

Question 13

3.1.6

How can some small organisms ‘walk on water’

Answer 13

The force of attraction between water molecules makes waters sufficiently dense for some smaller organisms to move along its surface

Question 14

3.2.1

Distinguish between organic and inorganic compounds

Answer 14

Organic compounds are compounds containing carbon found in living things, except hydrogen carbonates, carbonates and oxides of carbon
Inorganic compounds are all other compounds

Question 15

What Are carbohydrates?

Answer 15

Organic compounds, consisting of one or more simple sugars that as monomers follow the general basic formula of (CH2 O)x

Question 16

3.2.3

List three examples of a monosaccharide

Answer 16

Glucose, galactose, fructose

Question 17

3.2.3

List three examples of a disaccharide:

Answer 17

Lactose, maltose, sucrose

Question 18

3.2.3

List three examples of a polysaccharide

Answer 18

Cellulose, glycogen, starch

Question 19

3.2.4

State one function of glucose, lactose and glycogen in animals

Answer 19

Glucose:
A source of energy which can be broken down to form ATP via cellular respiration

Lactose:
A sugar found in the milk of mammals, providing energy for suckling infants

Glycogen:
Used by animals for short term energy storage (between meals) in the liver

Question 20

3.2.4

Explain one function of fructose, sucrose and cellulose in plants.

Answer 20

Fructose:
Found in honey and onions, it is very sweet and a good source of energy

Sucrose:
Used primarily as a transportable energy form

Cellulose:
Used by plant cells as a strengthening component of the cell wall

Question 21

What is a lipid? Name three common lipids

Answer 21

A group of organic molecules that are insoluble in water but soluble in non-polar organic solvents

Triglycerides, phospholipids and steroids

Question 22

3.2.6
State three (out of five) functions of lipids

Answer 22

Structure: phospholipids are a main component of cell membranes
Hormonal signalling: steroids are involved in hormonal signalling (e.g. Oestrogen, preogesterone, testosterone)
Insulation: fats in animals can serve as heat insulators while sphingolipids in the myelin sheath (of neurons) can serve as electrical insulators
Protection: triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury
Storage of energy: triglycerides can be used as a long term energy storage source

Question 23

3.2.7

Compare the use of carbohydrates and lipids in energy storage

Answer 23

Similar:
Complex carbohydrates and lipids both contain a lot of chemical energy and can be used of energy storage.
Complex carbohydrates and lipids are both insoluble in water - they are not easily transported
Carbohydrates and lipids both burn cleaner that proteins

Differences:
Lipid molecules contain more energy per gram than carbohydrates
Carbohydrates are more readily digested that lipids and release their energy more rapidly
Monosaccharides and disaccharides are water soluble and easier to transport to and from storage sites than lipids
Animals tend to use carbohydrates primarily for short term energy storage, while lipids are used for more long term storage
Carbohydrates are stored as glycogen in animals, while lipids are stored as fats
Lipids have less effect on osmotic pressure within a cell than complex carbohydrates

Question 24

What are proteins?

Answer 24

Large organic compounds made of amino acids arranged in a linear chain

Question 25

3.3.2 | What are the names of the four bases in DNA? How do they pair up?

Answer 25

Adenine & thymine | Guanine & cytosine

Question 26

3.4.1 Explain DNA replication in terms of unwinding of the double helix and separation of the strands by helicase, followed by the formation of the new complementary strands by DNA polymerase

Answer 26

Helicase: Unwinds the DNA and separates the two polynucleotide strands by breaking the hydrogen bonds between complementary base pairs The two separated polynucleotide strands act as templates for the synthesis of new polynucleotide strands DNA polymerase: Synthesis new strands from the two parental template strands Free deoxynucleoside triphosphates are aligned opposite their complementary base partner are covalently bonded together by DNA polymerase to form a complementary nucleotide chain The energy for this reaction comes from the cleavage of the two extra phosphate groups

Question 27

3.4.2 | Explain the significance of complementary base paring in the conversation of the base sequence of DNA

Answer 27

Each of the nitrogenous bases can only pair with its complementary partner (a=t, g=c) Consequently, when DNA is replicated by the combined action of helicase and DNA polymerase: The new strands formed will be identical to the original strands separated from the template The two DNA molecules formed will be identical to the original molecule

Question 28

3.4.3 | How is DNA replication semi-conservative?

Answer 28

Because when a new double strand DNA molecule is formed: One strand will be from the original molecule One strand will be newly synthesised

Question 29

3.5.1 | Compare the structure of DNA and RNA

Answer 29

DNA has the sugar deoxyribose, RNA has the sugar ribose. DNA has the base thymine, and RNA has uracil. DNA is double stranded and RNA is usually single stranded. DNA forms a double helix and RNA does not

Question 30

3.6.1 | Define enzyme

Answer 30

A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold

Question 31

3.6.1 | Define active site

Answer 31

The site on the surface of an enzyme which binds to the substrate molecule

Question 32

3.6.2 | Explain enzyme substrate specificity

Answer 32

Active site and substrate complement each other in terms of both shape and chemical qualities (e.g opposite charges) Binding to the active site brings the substrate into close physical proximity, creating an enzyme substrate complex The enzyme catalyses the conversion of the substrate into a product(s) creating an enzyme product complex As the enzyme is not consumed in the reaction it can continue to work once the product dissociates

Question 33

3.6.3 | Explain the effects of temperature on enzyme activity

Answer 33

Low temperatures result in insufficient thermal energy for the activation of a given enzyme-catalysed reaction to be achieved Increasing the temperature increases the speed and motion of enzyme and substrate --> higher enzyme activity, higher kinetic energy results in mor frequent collisions between enzyme and substrate. At optimal temperature the rate of enzyme activity will be at its peak Higher temperatures can cause enzymes to denature

Question 34

3.6.3 | Explain the effects of pH on enzyme activity

Answer 34

Changing the pH will alter after the charge of the enzymes which in turn will protein solubility and may change the shape of the molecule Changing the shape of the active site will diminish it's ability to bind to the substrate Enzymes have an optimum pH and moving outside of this range will result in a diminished rate of reaction

Question 35

3.6.3 | Explain how substrate concentration effects enzyme activity

Answer 35

Increasing substrate concentration will increase the activity of a particular enzyme. More substrate means there is an increased likelihood of enzyme substrate collisions and reactions After a certain point the rate of reaction will cease to rise as the environment would becoMe saturated and all enzymes are bound and reacting

Question 36

3.6.4 | Define denaturation

Answer 36

Structural change in a protein that results in the loss (usually permenant) of its biological properties Can be caused by heat or pH

Question 37

3.7.1 | Define cell respiration

Answer 37

Controlled release of energy from organic compounds in cells to form ATP

Question 38

3.7.2 | What happens to glucose in the cytoplasm during cell respiration?

Answer 38

Glycolysis - the breakdowns of one molecule of glucose (6C) into two molecules of pyruvate (2 * 3C) with a small net yield of ATP (2 molecules of ATP) This process also results in the reduction of two hydrogen acceptors to form two molecules of NADH + H+

Question 39

3.8.1 | What is photosynthesis? Outline the two stages.

Answer 39

The process by which plants synthesise organic compounds in the presence of sunlight. 1) the light dependant reactions convert the light energy into chemical energy (ATP) 2) the light dependant reactions use the chemical energy to synthesised organic compounds The organic molecules produced in photosynthesis can be used in cellular respiration to provide the energy needed by the organism

Question 40

3.8.2 | What colours is sunlight made up of?

Answer 40

``` Red Orange Yellow Green Blue Indigo Violet ```

Question 41

3.8.3 | What is chlorophyll?

Answer 41

The main site of light absorption in the light dependant stage of photosynthesis There are a number of different chlorophyll molecules, each with their own distinct absorption spectra The main photosynthetic pigment, that absorbs light energy and release electrons which are used to make ATP.

Question 42

3.8.4 | Outline the difference in absorption of red, green and blue light by chlorophyll

Answer 42

The main colours of light absorbed by chlorophyll are red and blue light Main colour not absorbed is green (it's reflected) Explains why leaves are green. Excepting when the prescience of other pigmented substances produces a different colour

Question 43

3.8.7 | How can you measure carbon dioxide uptake in photosynthesis?

Answer 43

CO2 uptake can be measured by placing a plant in an enclosed space with water Carbon dioxide interacts with the water molecules, producing bicarbonate and hydrogen ions, which increases the acidity of the resulting solution The change in pH can therefore provide a measure of CO2 uptake by a plant

Question 44

3.8.7 | How can you measure oxygen production at different rages of photosynthesis?

Answer 44

Oxygen production can be measured by submerging a plant in an enclosed space with water attracted to a sealed gas syringe An oxygen gas produced will bubble out of solution and can be measured by a change in water level

Question 45

3.8.7 | How can the rate of photosynthesis be measured indirectly by an increase in biomass?

Answer 45

Glucose production can be indirectly measured by a change in the plant's biomass. This requires the plant to be completely dehydrated prior to the weighing to ensure the change in biomass reflects a change in organic matter not water content Or to determine the change in starch levels in a plant, starch can be identified by iodine staining and quantitated using a colorimeter

Question 46

3.8.8 | Outline the effect of temperature of the rate of photosynthesis

Answer 46

Photosynthesis is controlled by enzymes which are sensitive to temperature As temperature increases the rate of photosynthesis will increase as reagents have greater kinetic energy and are more likely to react. above a certain temperature, the rate of photosynthesis will decrease as essential enzymes begin to denature

Question 47

3.8.8 | Explain how light intensity affects photosynthesis

Answer 47

As light intensity increases the rate of photosynthesis will increase up until a certain point, when photosynthesis is proceeding at its maximum rate Further increases to light intensity will have no effect on photosynthesis as chlorophyll at saturated by light Different wave lengths of light will have different effects on rate of photosynthesis

Question 48

3.8.8 Outline the effect of carbon dioxide concentration on the rate of Photosynthesis

Answer 48

As the concentration of carbon dioxide increases, the rate of photosynthesis will increase up until a certain point, when photosynthesis is proceeding at its maximum rate Further increases to carbon dioxide concentration will have no effect on photosynthesis, as the enzymes responsible for carbon fixation become saturated