Other Biology Answers

Student prepared to start a culture using 2.5*10^-3g yeast cells in 1d^m3 nutrient broth.

The average mass of yeast cell is 2*10 ^-11g.

calculate the number of cells in the starter culture 

Give your answer in standard form 

 A light microscope can be used to observe yeast cells.

 State the equipment that would be needed in addition to a microscope to measure the average time diameter of yeast cells.

The student wanted to study the effect of the different sugars in the rate of growth of a yeast population.

They used to colorimeter to measure the absorbance of a culture of yeast cells.

The absorbance of the yeast culture is proportional to the concentration of yeast cells.

As the yeast is multiplied it was necessary to dilute the sample to obtain a reading on the colorimeter.

Describe how the student could 1cm³ cubed pippets and 10cm³ measuring cylinders to dilute the sample so that it was 10,000 times less concentrated .

A student stated:

• The rates of respiration with glucose maltose and sucrose were very similar.
• The yeast could not hydrolyse diasaccharides.

Evaluate the students statements.

The sensory neurone was stimulated electrically and the FURA-2 fluoresence in the synaptic bulb was measured. At the same time an electrode recorded the membrane potential in a postsynaptic neurone. The results of this study are shown below:

Strengths of electrical

stimulation  Low Medium High

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FURA-2 fluoresence in

synaptic bulb Low Medium High

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Highest membrane potential

in postsynaptic neurone (mV) -60 +40 +40

The intesity of FURA-2 fluorescence is proportional to the concentration of Ca²⁺ ions.

The scientists concluded that changes in the concentration of Ca²⁺ ions in the presynaptic neurone caused an action potential in the post synaptic neurone.

Evaluate and explain the scientists' conclusion.

Algae are single-celled photosynthetic organisms. An investigation was carried out into the effect of CO2 concentration on the concentrations of ribulose diphosphate (RuBP) and glycerine 3-phosphate (GP) present in algae. Algae were grown in a solution containing a high concentration of CO2. The concentration of CO2 was then reduced. RuBP and GP concentration were measured for 2 minutes before and 3 minutes after the reduction in CO2 concentration.

Describe and explain the effect of reducing the CO2 concentration of RuBP and GP in the algae.

The student used a colorimeter to measure the concentration of each substance in the liquid surrounding the cells.

The colorimeter had an analogue display. The reading was indicated by a needle moving across the scale. The smallest divisions on the scale corresponded to 0.1 absorbance unit.

After the investigation the students suggested some improvements.

Match each of the improvements to the corresponding justification:

Improvements:

1) Use a colorimeter with a digital display showing absorbance units to three decimal places  

2) Cheque the zero value of the colorimeter with purified water before use 

3) For each concentration repeat the measurement of the rate of reaction three times and calculated mean ask 4) Students in several schools to carry out the same investigation 

Justification:

A) To assess repeatability 

B) To assess reproducibility 

C) To reduce systematic error 

D) To reduce random error (uncertainty)

E) To increase resolution 

What type of graph (rate of uptake against concentration) would a substance entering a cell by diffusion produce?

What alternatively what type of graph would a substance entering a cell by active transport produce?

Which of the following statements A to D describes and explains the relative yield of ATP in anaerobic and aerobic respiration?

A)   Anaerobic respiration produces less ATP per molecule of glucose because lactate is converted to pyruvate

B)   Anaerobic respiration produces less ATP per molecule of glucose because NAD is not regenerated in oxidative phosphorylation

C)   Anaerobic respiration produces more ATP per molecule of glucose because NAD is regenerated in oxidative phosphorylation 

D)   Anaerobic respiration produces more ATP per molecule of glucose because pyruvate is converted to lactate 

Which of the following statements from A to D about water transport in plants is/are correct?

1- Transpiration happens as a consequence of the need for gas exchange.

2- There are cohesive forces between water molecules because they from hydrogen bonds with one another.

3- Water is drawn up from the stem due to adhesive forces between water molecules.

A) 1, 2 and 3

B) only 1 and 2

C) only 2 and 3

D) only 1