Exam Long Answer Questions IB Bio HL/SL

Disscuss how skeletal muscle fibers are an exception to the cell theory

are larger, have many nuclei, are not typical cells

Disscuss how fungal hyphae are an exception to the cell theory

not always divided into single cells

Disscuss how unicellular organisms are an exception to the cell theory

can be acellular, larger than typical cell, carry out all functions of life

Disscuss how some tissue organs are are exceptions to the cell theory

some are extracellular e.g. xylem in trees

Eukaryotic cells have inter and extracellular components. State the function of one named extracellular component

-plant cell wall strengthens and supports the cell from gravity

Explain how the surface area to volume ratio influences cell size

- small cells have a larger ratio than larger cells and surface area to volume ratio increases with size

- the cells membrane must be large enough to absorb nutrients and excrete waste as needed

- the amount of materials a cell needs is dependent on cell volume

Outline differentiation of cells in multicellular organisms

-differentiation is the development of a cell in a specific way

- cells carry out specific functions

- cells have all genes and could develop in any way

- because of this only some genes are expressed while others are not

- tissues are groups of differentiated cells

Describe the importance of stem cells in differentiation

- stem cells are undifferentiated

- stem cells come from embryo and some adult cells

- stem cells are pluripotent meaning they can differentiate in many ways

- some genes are expressed

Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes

- the phospholipid structure helps due to its hydrophilic tail and hydrophilic head

- tail is made of glycerol and phosphate and the head is made of 2 fatty acids

- phospholipids arrangement in the membrane helps because the phosholipids form a bilayer where the hydrophilic heads face the outside and the hydrophobic tails face the inside

Explain the role of of vesicles in transporation of materials within cells

- vesiclesare membrane bound and formed by pinching off part of a membrane

- vesicles can carry proteins which are synthesised by endoplasmic reticulum

- proteins accumulate in the ER and translated to the Golgi Apparatus for processing

- these proteins are transported to specific organelles

- they then fuse with an organelles membrane so the vesicles content joins the organelle

- these are transported to the plasma membrane and fuses

Describe the process of active transport

- active transport uses energy and goes against concentration gradient , low to high

- active transport requires a carrier protein in the cell membrane

- hydrolysis occurs, ATP - ATP + Phosphate

- confirmational change of the protein

Outline the ways in which substances move passively across membranes

- diffusion - passive transport across membrane

- facillitated diffusion - channel proteins allow hydrophilic particles across a membrane

- down the concentration gradient - high to low

- osmosis - diffusion of water across a membrane from region of lower solute concentration to higher

Explain the functions of the different tissues of a leaf

- cuticle - prevents water loss

- epidermis - protects cell inside

- stomata - gas exchange

- palisade mesophyll - layer for photosynthesis

-air space - diffusion of gases

xylem - water transport, minerals

- guard cells - open + close stomata

Explain the role of auxin in phototropism

- auxin is a growth hormone in plants

- it is produced by the shoot tip

- causes transport of hydrogen ions from cytoplasm to the cell wall

- this creates a decrease in PH and H+ pumping breaks the bonds between cell wall fibers

- cell walls become flexible

- auxin hormone causes cells to grow and alters gene expression

- phototropism is the growth towards light, the shoot tip senses the brightest light source and grows in the direction of it

- auxin move to the side with the least amount of light

- cells on the dark side grow

Outline the adaptations of plant roots for absorption of mineral ions from the soil

- mineral ions are absorbed by active transport

- one adaptation is their large surface area which is increased by branching

- another adaptation is root hairs, root hair cells have carrier proteins and many mitochondria which provide ATP for active transport

Describe the process of mineral ion uptake into roots

- mineral ions are absorbes by root hairs throught the epidermis

- root hairs increase surface area for absorption

- active transport which requires energy is used

- protein pumps are used to move ions across membranes against the concentration gradient

- these specific ions enter the cell wall space and are absorbed

Explain how water is carried by the transpiration stream

- transpiration is water lost by plant by evaporation

- water flows from roots to leaves through the xylem

- water is evaporated through spongey mesophyll cells and replaces by osmosis from xylem

- water vapor is diffused through the stomata

- water that is pulles out of xylem creates low pressure and suction causinf the transpiration pull

- water and xylem adhere because water is polar and this creates as continous stream

Explain how abiotic factors affect the rate of transpiration in a terresterial plant

- less transpiration occurs as humidity rises

- this affects a plants concentration gradient by making it smaller

- more transpiration occurs as temperature rises, making diffusion faster

- more transpiration occurs as wind speed increases which increases the concentration gradient of water vapor

- more light makes more transpiration since light casues stomata to open

List three abiotic factors which affect the rate of transpiration in a terrestrial plant

- light

-temperature

- wind

Explain how wind affects the rate of transpiration from a leaf

- wind affects the rate of transpiration

- wind blows water vapor away from the leaf

- water vapor that diffuses pout of the stomata is carried out

-low humdity that is maintained near the leaf becomes saturated without wind

- there is a large water confentration gradient between the inside and outside of the leaf

- diffusion of water vapor is rapid, making transpiration rapid

- wind has no effecr if the air brought by the wind is already saturated

Outline adaptations of xerophyte

- xerophytes live in dry conditions

- they have spines to prevent water loss by trans piration

- rolled leaves to prevent water loss

- thick waxy cuticle prevent water loss by transpiration

- deep, widespread roots to obtain more water

Outline the role of the phloem is the active translocation of bischemicals

- phloem is living tissue

- it is composed of companion cells that are invovled in ATP production

.amino acids ,products of photosynthesis are transported bidirectionally

- nutrients move from source to sink

- the movement of water into the phloem causes transport, this is called the pressure flow hypothesis

describe the metabolic events of seed germination in a starchy seed

- first water is absorbed

- respiration is increased by the embryo and GAs are secreted

- the producton of amylase is stimulated

- starch is digested into smaller sugars

- nrutrients are transported to the emryo

Explain the conditions needed for seed germination

- water is needed

- causes swelling which bursts the seed coat

- soluble food reserves are mobilised and the cell is rehydrated

- food reseve is transported as well as growth hormones

- growth inhibitors are washed out by water

- oxygen is needed

- required for aerobic respiration

this provides ATP for metabolic activity

- warmth needed

-increases enzyme activity

-fire breaks down inhibitors

- chilling breaks down inhibitors

- light breaks down inhibitors and stimulates germination

Explain how flowering is controlled in long day and short day plants

- flowering is affected by light

- phytochromes pfr and pr

- pr- red light

- pfr- far red light

- sunlight has more red than far red light so pfr is more active during the day

- reversion of pfr to pr occurs in darkness

- pfr active

- pr inactive

- long day plants, flowering is induced by dark periods and are shorter than a critical length

- enough pfr remains in long-day plants at the end of short nights to stimulate flower growth

- pfr promotes flowering in long day plants

- short day plants flower in dark periods

- enough pfr is converted to pr at the end of long nights to promote flowering

- pfr acts as inhibitor of flowering in short-day plants

Outline the process of glycolosis

-glycolosis occurs in the cytoplasm of cells

- first, hexose is phosphorylated using ATP

- next, hexose phosphate is split into 2 triose phosphates, lysis

- one product is reduced NAD - NADH +H+

- second product is 2 ATP produced

- last product is pyruvate

Explain how the structure of mitochondrion allows it to carry out its function efficiently

- compartmentalised membranes to seperate processes in the cytoplasm

- small size and large surface area to volume ratio

- allows rapis intake and release of minerals

- the matrix contains enzymes that carry out the krebs cycle

- the inner membrane forms cristae and contains ATP synthase

- ATP synthase produce ATP

- the gap between the inner and outer membrane space is where a proton gradient is formed rapidly

- this makes chemiosis more efficient

- the inner membrane contains the electon transport pathway

Explain the reactions that occur in the matrix of the mitochondrion that are part of aerobic respiration

- pyruvate is decarboxylated and CO2 is removed

- this pyruvate is used in the link reaction where it combines with coA to form acetyl coA

- this pyruvate is oxidised and hydrogen is removed

- following this NAD is reduced to NADH + H+

- this is called oxidative phosphorylation

- after this the krebs cycle takes place

Explain the process of aerobic respiration

- aerobis respiration requires oxygen

- first glycolosis occurs and glucose is broken

down into 2 pyruvates

- a small yield of ATP; and oxidised NADH +H+ - NADH are produced

- next, pyruvate from glycolosis is converted to acetyl coA

- oxidative phosphorylation occurs, NADH and CO2 are formed

- fatty acids are converted to acetyl coA and enter the krebs cycle

- small yield of 1 ATP per cycle is produced

- FADH2 reduced to FADH + H+

- NADH reduced to NADH + H+

- electrons collect molecules which pass electrons to the electron transport chain

- oxygen finally accepts electrons to produce water

- the electron transport chain creates an electrochemical gradient and chemiosis powers ATP production

Outline the role of oxygen in providing cells with energy

- oxygen is needed for aerobic respiration but not for anaerobic respiration

- oxygen is used in oxidative phosphorylation

- oxygen also accepts protons to form water using oxygen

- water ALLOWS:

> more electrons along the ETC

> oxidation of NAD

> ATP production

> high yield of ATP from glucose in ATP

Exolain how chemisosis assists in ATP production during oxidative phosphorylation

- chemisosis is the movement of hydrogen ions across a membrane

- chemiosis occurs in the cristae

- chemiosis occurs during aerobic respiration

- oxidative phosphorylation occurs during the electron transport chain

- electrons are passed bwtween carriers and energy is released

- these electrons (H+) join with water to produce water

- protons move against the concentration gradient into the thylakoid space

- protons flow back into the matrix

- these protons pass through ATP synthase:

> ADP+PI >> ATP forms

Explain the similarities and differences in anaerobic and aerobic respiration

- similarities:

> both can start with glucose

> both use glycolosis

> both produce pyruvate

> co2 is produced

-differences:

aerobic

> pyruvate is transported to mitochondrion

> oxidised to co2 and water in the Krebs Cycle

> produces 36-38 ATP

> can use other compounds for energy

anaerobic

> fermentation produces lactic acid (humans) and yeast and co2 (others)

> produces 2 ATP

> occurs in the cytoplasm

> recycles NADH

Describe the central role of acetyl coA in carb and fat metabolism

- acetyl coA enters the Krebs Cycle

- carbs are converted to pyruvate in glycolosis

- pyruvate enter mitochondrion and is converted to acetyl coA

- hydrogen and co2 are removed by oxidative phosphorylation

- lipids enter the mitochondrion and are oxidised to acetyl coA

Explin the structure of DNA including its subunits and the way they are bonded together

- subunits of DNA are nucleotides

- conatin 1 base, 1 phosphate and 1 deoxyribose sugar

- there are 4 bases, adenine, thymine, cytosine and guanine

T>>A G>>C

- nucleotides link with sugar phosphate bonds

- two strands of nucleotides link together in 5' to 3' direction , antiparallel

- each base is paired to another by hydrogen bonds

Explain the process of DNA replication

- occurs in interphase of mitosis

- is semi-conservative

- first, the double helix is unwinded by DNA helicase and hydrogen bonds

- each strand of parent DNA id used as a template for synthesis

- pairs are added according to complimentary base pairing, adenine with thymine and cytosine with guanine

- DNA polymerase form new complimemtary strands using th existing strands as a template

Explain how DNA replication depends on the structure of DNA

- DNA is double stranded

- hydrogen bonds that link the strands can be easily broken

- DNA can split into two strands by helicase

- helicase moves progressively down the molecules

- backbones are linked by strong covalent bonds

- strands do not break and the base sequence is semi conserved

- base pairing is complimentary, Adenenine w/ Thymine, Cytosine w/ Guanine

- the two original strands carry the same information

- the two new strands have the same base sequence as the 2 original ones and they are polar

Describe the genetic code

- composed of mRNA base triplets called codons

- 64 different codons

- each codes for an additional amino acid tos growing polypeptide chain

- genetic code is degenerate meaning that more than 1 codon can code for a certain amino acid

- genetic code is universal- the same in all organisms

- AUG is the start codon

- some codons code for the end of translation

Discuss the relationship between genes and polypeptides

- originally assumed that 1 gene codes for 1 polypeptide

- 1 gene is transcribed into 1 mRNA

- mRNA is translated by a ribosome to synthesise a polypeptide

- there are many exceptions to one gene - 1 polypeptide found

> many more proteins than genes

> some genes don't code for polypeptides

> some code for tRNA, rRNA

> some genes regulate gene expression

> polypetides may be altered before they become proteins

Explain the advantages and disadvantages of a universal genetic code to humans

- advantages

> genetic material can be transcribed between species and humans

> one species could use a needed gene from another species

> livestock can be produced

- disadvantages

> viruses can invade cells and take over genes

> viruses cause disease

Distinguish between RNA and DNA

- DNA

> doube helix

> deoxyribose sugars

> 1 form being double helix

RNA

> single standed

> ribose sugars

> several forms - tRNA; rRNA etc.

Describe the roles of tRNA, mRNA and ribosomes in translation

- mRNA provides codons

- tRNA provide anticodons and an attached amino acid

- ribosome has two subunits and holds mRNA - start codon

- 2 tRNA molecules attach to mRNA on ribosome

- a peptide bond exists between amino acids on tRNA and a polypeptide forms

- this process continues until a stop codon is reached

- a polypeptide is released

Explain the process of translation

- mRNA binds to subunits of the ribosome

- ribosomes move down mRNA to the start codon

- the anticodon of tRNA pairs with the codon of mRNA

- complimentary base pairing between the anticodon and the codon occurs

- the anticodon of tRNA pairs with AUG the start codon

- 2nd tRNA pairs with the next codon

- a peptide bond forms between an amino acid

- the ribosome moves along mRNA by one codon

- tRNA loes amino acid and detaches

- another tRNA that loses its amino acid detaches

- this continues until the stop codon is reached

Outline the thermal, cohesive and solvent properties of water

- water has a high specific heat capacity

- a large amount of heat causes a small increase in temperature

- water has a high latent heat of vaporization

- a large amount of energy is needed to vaporize water

- hydrogen bonds between water molecules make them cohesive giving water a high surface tension explaining how water rises up xylem

- water molecules are polar making water a good solvent

Describe the significance of water to living organisms

- waters surface tension allows somw organisms

- polarity of water helps transport water

- transparency allows plants to photosynthesise in water/animals to see

- excellent solvent - can transport substances for transport in organisms

- thermal properties such as high heat of vaporisation makes water an excellent coolant

- buoyancy supports organisms

- provides habitat for aquatic organisms

Describe the use of carbs and lipids for energy storage in animals

- carbohydrates

> stored as glycogen in the liver

> short term energy storage

> can be released more quickly than lipids

> more soluble in water, more easily transported

- Lipids

> stored as fat in animals

> more energy per gram

> long term energy storage

> insoluble in water, less osmotic

List the functions of lipids

- source of energy

- heat insulation

- protection of internal organs

- water proofing

- buoyancy

- electrical insulation

- hormones - steroids

- glycolipid receptors

Lactose is widely used in food processing. Explain 3 reasons for converting lactose to galactose and glucose

- allows people who are lactose intolerant to consume milk

- reduces need for additional sweetner

- galactose and glucose are more soluble than lactose, smoother texture

In food processing, lactase is used at a low temperature of 5 degrees c. Suggest reasons for this.

- enzymes last longer at lower temperatures

- lower energy costs, takes less energy to acheive 5 degrees compared to 48 degrees c

- reduces bacterial growth and milk spoilage

- to control the rate of reaction

Outine how enzymes catalyze reactions

- enzymes increase the rate of chemical reactions

- enzymes allow a lower activation energy which is needed to overcome the energy barrier preventing the reaction

- substrate joins the enzyme at the active site forming an enzyme-substrate complex

- active site is specific for a certain substrate

- enzyme that binds with the substrate brings reactants closer together

- this facillitates chemical reactions

- an enzymes confirmation changes when the enzyme substrate complex CANNOT form therfore altering/breaking active sites and ionic bonds

Explain the effect of PH on enzyme activity

- enzymes have an optimal PH

- enzyme actitiy is lower above and below this optimum PH

- too acid or too base can denature enzymes

- the shape of the active site can be changes by this and the substrate can no longer bind to the active site and the enzyme-substrate complex cannt form

Outline enzyme substrate specificity

- active site of enzyme binds to specific substrate

- the shape of the active site and substrate compliment each other

- active site is not rigid and the substrate can induce slight changes in shape allpwing substrates of similar structure to bind with the same enzyme, induced fit

- this causes weakening of bonds in the substrate to lower activation energy

Outline the effect of temperature, light intensity and CO2 concentration on the rate of photosynthesis

- light

> rate of photosynthesis increases as light intensity increases

> rate reaches a plateu at high light levels

- CO2

> photosynthetic rate reaches a plateu at high CO2 levels

> rate levels of up to a maximum

- temperature

> rate increases with an increase in temperature up to an optimum level

> hight temperatures reduce rate of photosynthesis

Explain how the rate of photosynthesis can be measured

- equation:

CO2 + H2O > CH2O + O2

- the amount of co2 abosorbed per unit of time can be measured

- increase in biomass per unit of time can be measured

- o2 excretion can be measured

- Methods:

> volume of o2 bubbles per unit can be measured

> dry mass can be measured

> PH indicator can be used to monitor co2 uptake in water

Outline the differences in the absorption of different wavelengths of light by chlorophyll

- visible light is a range of wavelengths which have different colors and energy levels

- chlorophyll absorbs some for photosynthesis and reflects some

- red and blue light are absorobed the most

- green light is reflected and not used for photosynthesis

State the products and reactants of photosynthesis

- reactants

> co2, water, light

- products

> organic molecules like sucrose and glucose, o2

Define habitat, population, community and ecosystem

- habitat - the environment in which a species normally lives

- population - a group of organisms of the same species living and interacting in the same area at the same time

- community - a group of organisms and populations living and interacting with each other in an area

- ecosystem - a community and its abiotic environment

Compare the ways in which autotrophic, heterotrphic and sapotrphic organisms obtain energy

- autotrophs use an external non-organic energy source

- some autotrophs use light and photosynthesis to make their own food

- some autotrophs use inorganic chemical reactions to obtain energy

- heterotrphs obtain energy from other organisms

- heterotrophs usually consume food

- sapotrophs obtain energy from non-living matter like dead organisms

- sapotrophs digest oranic matter extracellularly

Describe what is meant by a food chain using an example with four named organisms

- food chains describe the feeding relationships between species

buffalo grass > 2 striped grass hopper > grass stick neat rat > black rat snake

producer > primary consumer > secondary consumers > teritiary consumers

Explain using an example of a food chain, how trophic levels can be deduced

phytoplankton > zoo plankton > sardine fish > tuna fish

- trophic level is a position in the movement of energy through an ecosystem

- phyto plankton the producers at the first trophic level capture energy throught photosynthesis

- zoo plankton the primary consumers at the second trophic level feed on phytoplankton

- sardine fish the secondary consumers at the 3rd trophic level feed on zoo plankton

Outline what is meant by the trophic level of an organism with three examples from a named habitat

- trophic level is the feeding level for an organism in a food chain

- this consists of producers, primary consumers, secondary consumers

- habitat - ocean

- phytoplankton, jelly fish, squids

Explain the flow of energy between trophic levels in ecosystems

- sunlight is the initial source of energy in most ecosystems

- energy from the sun is converted into potential energy by producers through photosynthesis

- energy escapes an ecosytem as heat

- energy flow is measured as energy per unit area per unit time > kJ m -2 yr -1

- energy is passed along trophic levels

- primary consumers obtain energy from plant food

- secondary and teritiary consumers obtain energy by eating other animals

- energy transfer between trophic levels is only 10% efficient because some energy is lost as heat through respiration

- decomposers obtain energy from waste products and dead organic matter

Describe the movement of energy and nutrients in an ecysystem

- an ecosystem is a community and its abitotic environment

- solar energy is first collected by plants

- energy moves through trophic levels via food

- only 5-20% is transferred between trophic levels, never 100%

- this is because energy is lost ad metabolic heat

- organisms absorb nutrients from food and the environment

- nutrients are complex organiy matter in organisms

- after organisms die decomposers break down complex organic matter into simpler substances which are then absorbed by plants and recycled

Explain the relationship bewteen rise in co2 concentration and the greenhouse effect

- greenhouse gases

> water vapor

> co2

> methane

> oxides of Nitrogen

- all of these gases occur naturally

- human activity has increased the normal level of these gases in recent years

- short wave radiation entering the Earth's atmosphere is reradiated as longer wave infared radiation, higher to lower energy in the form of heat

- this increases atmospheric temperature

- this increase is at a higher rate than normal creating an imbalance which threatens ecosystems

- the Earth has had many flucuations in gas levels in the past