Light Microscope Essay

1. Light Microscope Electron Microscope

Cell Components Seen cell walls, vacuoles, cytoplasm, chloroplasts, nucleus and plasma membrane. Cell structure and ultrastructure of organelles such as cell wall, nucleus, nucleolus, vacuoles, mitochondria, rough and smooth endoplasmic reticulum, cell membrane, chloroplast, Golgi apparatus, and ribosomes can be seen.

Specimen Preparation Simple procedure required and involves staining Procedure is harsh.

Illumination Visible light rays are focused by glass lenses. Electron beams deflected by electromagnets.

Image Formation Due to absorption of light waves. Electrons scatters to form the image.

Magnification Magnification is up to 4000x. 300,000x magnification can be achieved.

Resolution Resolution is 0.25 µm or 250 nm (2500 Å).

(a) (i) Fick’s law:

((rate of) uptake / diffusion is proportional to (surface area ×difference in concentration)/(thickness of membrane) (ii) Rate of uptake is proportional to concentration of glucose. (b) (i) Carrier/transporter protein molecules are still available to bind if more glucose added. Therefore, glucose is a limiting factor; (ii) Transporters are saturated and are limiting factor.

6. (a)

Feature Mitosis Meiosis

(i) Involves two successive nuclear divisions   (during reduction and cell division)

(ii) Chromosomes replicate before they are seen in stained cells.  (can be seen during S1 phase) 

(iii) Involves the formation of chiasmata.   (during Prophase I; formed due to crossing over)

(iv) Leads to random assortment of chromosomes.   (shuffling of complete chromosomes)

(v) Involved the separation of the sister chromatids.  (during Anaphase)  (during Anaphase II)

(vi) Occurs during gamete formation in humans.   (reducing the copy number of chromosomes to half)

(vii) Splitting of centromere is followed by anaphase.   (during Meiosis II)

(viii) Daughter nuclei have identical genetic composition.  (copy number of the parent cell is duplicated before separation.)