cell structure

State a development in electron microscopy that has improved the study of cell ultrastructure.(1)

freeze-fracture/cryogenic electron microscopy/fluorescent stains/ immunofluorescence;

Suggest a reason for using a lower power objective lens when first focusing on a slide under the microscope (1)

1.   it is easier to find the specimen using a low power objective lens
     OR
     there is a larger field of view/depth of focus;

2.   it is easier to locate the most interesting part of the specimen with a low power objective lens;

3.   most microscopes are calibrated so that once in focus using the low power objective lens they will be close    to focus using the higher power, so this helps focusing;

4.   reduced risk of cracking the slide;

Outline the cell theory (2)

a. cells can only arise from preexisting cells ✔

b. living organisms are composed of cells/smallest unit of life ✔

c. organisms consisting of only one cell carry out all functions of life in that cell/cells perform life functions «at some point in their existence» ✔

d. although most organisms conform to cell theory, there are exceptions ✔

Distinguish between the structure of chromosomes in prokaryotes and eukaryotes (2)

1. prokaryotes (usually) have one chromosome while eukaryotes have numerous chromosomes;

2. prokaryotes have a circular chromosome while eukaryotes have linear ones;

3. eukaryotes’ chromosomes are associated with histones/proteins but prokaryotes/Eubacteria have naked DNA vs eukaryote DNA associated to proteins/histones;

Testis cells are eukaryotic cells. Identify the structures seen under the electron microscope in testis cells that are not present in prokaryotic cells. (4)

a. nucleus/nuclear membrane ✔

b. membrane bound organelles ✔

c. mitochondria ✔

d. rough ER/smooth ER/golgi apparatus ✔

e. lysosomes / centrioles ✔

f. large/80S ribosomes / ribosomes attached to a membrane ✔

g. linear chromosomes / histones ✔

Outline the structures in M. tuberculosis (prokaryote) that are not present in a human cell. (3)

a. cell wall ✔

b. pili/flagella ✔

c. 70S ribosomes ✔

d. nucleoid / circular DNA
OR
naked DNA ✔

e. plasmids ✔

Outline the structural and genetic characteristics of eukaryotic chromosomes (4)

a. linear/not circular DNA molecule
OR
one chromosome is one molecule of DNA/one chromosome is two DNA molecules «after replication» ✔

b. associated with histone proteins/nucleosomes ✔

c. centromere joins sister chromatids «after DNA replication» ✔

d. telomeres at the end «of the chromosome/chromatid» ✔

e. carries a sequence of genes / each gene occupies a specific locus ✔ Do not accept ‘sequence of bases’ for mpe.

f. alternative alleles of genes / homologous chromosomes carry same sequence of genes ✔

g. chromosomes in pairs / two «homologous chromosomes» of each type «in a diploid cell» ✔

h. non-coding sequences/example of a non-coding sequence ✔ Do not allow mph if the response states that chromosomes are always condensed.

i. supercoiled/condensed «during mitosis/meiosis» ✔

State two structural similarities between mitochondria and chloroplasts.

a. (a loop of) DNA ✔

b. 70S ribosomes ✔

c. double membrane ✔

d. electron transport chains/enzyme complexes in (internal) membranes ✔

e. enzymes in a region of fluid/in stroma and matrix ✔

f. large area of (internal) membrane/cristae and thylakoids ✔

State two functions of life (2)

a. nutrition ✔

b. metabolism/respiration ✔

c. growth ✔

d. response/irritability ✔

e. excretion ✔

f. homeostasis ✔

g. reproduction ✔

Describe the organelles and other structures in animal cells that are visible in electron micrographs (7)

1. plasma membrane is thin layer forming outer boundary;

2. cytoplasm fills space between membrane and nucleus;

3. nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;

4. chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);

5. mitochondria with cristae/double membranes;

6. (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;

7. endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;

8. Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;

9. vesicles which are small membrane sacs;

10. lysosome which contains enzymes/which is densely staining;

11. any other organelle that would be visible correctly described

Draw the ultrastructure of a prokaryotic cell (3)

a. cell wall;

b. plasma membrane; Clearly shown as a separate line under the cell wall or the inner line

c. cytoplasm AND 70S ribosomes; Do not allow (small) circles

d. nucleoid/naked DNA;

e. plasmid
OR
pili
OR
flagella/flagellum;