Biochemistry

Q & A on Cell Structure

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Q1: Which one of the following cell structures can be seen with a light microscope? (Mark 1)

A. mitochondrion

B. ribosome

C. rough ER

D. smooth ER

Ans: (A) Mitochondrion

Q2: The use of electrons as a source of radiation in the electron microscope allows high resolution to be achieved because electrons: (Mark 1)

A. are negatively charged.

B. can be focused using electromagnets.

C have a very short wavelength.

D travel at the speed of light.

Ans: (C) have a very short wavelength.

Q3: Which one of the following structures is found in animal cells, but not in plant cells? (Mark 1)

A. cell surface membrane

B. centriole

C. chloroplast

D. Golgi body

Ans: (A) cell surface membrane

Q4: Copy and complete the following table, which compares light microscopes with electron microscopes. Some boxes have been filled in for you.  (Mark 8)

FeatureLight MicroscopeElctron Microsope
source of radiation  
wavelength of radiation used about 0.005 nm
maximum resolution 0.5 nm in practice
lensesglass 
specimen non-living or dead
staincoloured dyes 
imagecolored 

Ans:

FeatureLight MicroscopeElctron Microsope
source of radiationlightelectron
wavelength of radiation used400-700nmabout 0.005 nm
maximum resolution200nm0.5 nm in practice
lensesglasselectromagnets
specimenliving or non-living 0r deadnon-living or dead
staincoloured dyesheavy metals
imagecolouredblack and white

Q5: List ten structures you could find in an electron micrograph of an animal cell which would be absent from the cell of a bacterium (Mark 10)

Ans:

  • nucleus
  • (smooth) endoplasmic reticulum
  • rough endoplasmic reticulum
  • 25 nm / larger / 80S ribosomes
  • linear / noncircular DNA
  • chromatin / chromosome(s)
  • lysosomes
  • Golgi body
  • mitochondrion / mitochondria
  • microtubule;
  • centriole
  • centrosome
  • vacuoles
  • microvillus / microvilli
  • cilium / cilia
  • nucleolus / nucleoli
  • nuclear envelope
  • nuclear pores 

Q6: Advice on answering question 6: If you are asked to distinguish between two things, it is likely that it is because they have certain things in common and that they may even be confused with each other. In your answer, it is helpful where relevant to point out similarities as well as differences. Remember that for organelles there may be differences in both structure and function. Distinguish between the following pairs of terms:

(A) magnification and resolution (Mark 3) 

(B) light microscope and electron microscope (Mark 2) 

(C) nucleus and nucleolus (Mark 4)

(D) chromatin and chromosome (Mark 3)

(E) membrane and envelope (Mark 3)

(F) smooth ER and rough ER (Mark 4)

(G) prokaryote and eukaryote (Mark 4)

Ans: 

(A) magnification is the number of times larger an image is compared with the real size of the object

resolution is the ability to distinguish between two separate points / the greater the resolution, the greater the detail that can be seen

a statement linking the terms, such as both terms used with reference to microscopy

(B) light microscope uses light as a source of radiation

electron microscope uses electrons as a source of radiation

(C) both organelles found in eukaryotic cells

nucleolus is located inside nucleus

nucleus controls cell activity

nucleolus makes ribosomes

e.g. nucleus surrounded by envelope, no membrane round nucleolus

(D) chromatin and chromosomes both contain DNA (and histones) found in nucleus

chromatin is the loosely coiled form of chromosomes

chromatin is the form that exists between cell divisions

chromosomes are formed just before nuclear division

(E) an envelope consists of two membranes (one just outside the other)

a membrane is a thin (partially permeable) barrier found around cells and some organelles

example of at least one organelle surrounded by an envelope is given

membranes found in all cells, envelopes only in eukaryotes

(F) both consist of flattened membrane-bound sacs

both found spreading through cytoplasm of eukaryotic cells

smooth ER lacks ribosomes, rough ER has ribosomes on surface

one function of smooth ER given e.g. makes lipid

rough ER transports proteins made by ribosomes on its surface

(G) prokaryotes have no nucleus, eukaryotes have nucleus

prokaryotes are smaller

prokaryotes have few organelles

eukaryotes have many organelles, some membrane bound 

one other important difference given evolved from prokaryotes 

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