Biology Answers

The endosymbiosis theory suggests that mitochondria may have evolved from bacteria that were takes inside other cells.

These cells then evolved into eukaryotes.

Give two structural features of mitochondria that support this theory

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.

With reference to the molecular structure of FURA-2, explain why FURA-2 is unable to cross cell membranes?

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 would happen if each vesicle does not fuse with the plasma membrane

What would be the effect of DNP on the uptake of a substance in a cultured cell. (the rate of uptake is directly proportional to the concentration of the substance)

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?

A teacher told his students that the human body makes the equivalent of its own mass in ATP everyday. Explain why at the end of the day only a small proportion of the students' mass was ATP.

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