2.1.1 Cell structures

Question 1

The use of microscopy to observe and investigate different types of cell and cell structure in a range of eukaryotic organisms

Question 2

The preparation and examination of microscope slides for use in light microscopy

Answer 2

To prepare slides they should be dehydrated, embedded in wax, very thin, stained and mounted.
An eyepiece graticule is found in the microscope, but the scale is arbitrary, so it needs to be calibrated for each different objective lens. A stage graticule is placed on the microscope stage. Usually each division in this ruler is 10 μm and the total length is 100 μm or 1mm. The value of each eyepiece unit can be worked out by lining the two up and dividing the value of the stage graticule by the stage graticule where they line up exactly.

Question 3

The use of staining in light microscopy

Answer 3

Staining is essential regarding identifying organelles within a cell. More so, as the Cytoplasm is transparent so it’s essential to apply stains (and counterstains) to the slide containing the specimen being examined under a light microscope - light passes through everything on the slide.
Differential staining: stains that bind to specific cell structures, staining each structure differently so the structures can be easily identified within a single preparation.
E.g. iodine in potassium iodide solution stains the cellulose in plant cell walls yellow, and starch granules blue/black (violet under the microscope) or acetic orcein staining DNA red.

Question 4

The representation of cell structure as seen under the light microscope using drawings and annotated diagrams of whole cells or cells in sections of tissue

Answer 4

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Question 5

What is the magnification formula?

Answer 5

Magnification=size of image/size of real object

Question 6

The difference between magnification and resolution

Answer 6

Magnification refers to the increase in size of an object when viewed through a microscope, while resolution refers to the ability of a microscope to distinguish between two separate objects that are close together.

Question 7

The ultrastructure of eukaryotic cells and the functions of the different cellular components

Answer 7

Houses the genetic material (DNA), together with the histone proteins in the chromosomes - suspended in the nucleoplasm. The nucleoplasm contains chromatin which is molecularly constructed of DNA and histone proteins.
The DNA contained within the nucleus, codes to produce enzymes and henceforth, controls chemical reactions (intracellular metabolism) within the cell. Enzymes control the chemical reactions within the cell.
Houses DNA responsible for protein synthesis
The nucleus is responsible for producing mRNA needed in cell division

Question 8

The ultrastructure of eukaryotic cells and the functions of the different cellular components; nucleolus

Answer 8

Responsible for, making rRNA, needed in order to make ribosomes. rRNA = ribosomal ribonucleic acid

Question 9

The ultrastructure of eukaryotic cells and the functions of the different cellular components; nuclear envelope

Answer 9

Controls the passage of material in and out of the nucleus. The membrane regulates the passage of macromolecules like proteins and RNA although, permits the free passage of water, ions, ATP and other small molecules.

Question 10

The ultrastructure of eukaryotic cells and the functions of the different cellular components; rough endoplasmic reticulum

Answer 10

Package and transport proteins made by the ribosomes – on the RER’s surface – into vesicles

Question 11

The ultrastructure of eukaryotic cells and the functions of the different cellular components; smooth endoplasmic reticulum

Answer 11

Site of lipid synthesis and henceforth, steroid hormones. Lipids are needed in the formation of steroid hormones.

Question 12

The ultrastructure of eukaryotic cells and the functions of the different cellular components; Golgi apparatus

Answer 12

Modifies proteins received from the Rough ER by adding carbohydrates to form glycoproteins and then packages them into vesicles so they can be transported.

Question 13

The ultrastructure of eukaryotic cells and the functions of the different cellular components; ribosomes

Answer 13

Ribosomes, in plant eukaryotic cells (80s) are slightly larger than those found in the likes of prokaryotic cells (70s). They’re always found in large quantities.
Site of protein synthesis inside the cell.
Ribosomes free in the cytoplasm, synthesize enzymes used in the cytoplasm e.g. those used in glycolysis

Question 14

The ultrastructure of eukaryotic cells and the functions of the different cellular components; lysosomes

Answer 14

Release a hydrolitic enzymes, that can destroy specific “old” organelles within the cell.

Question 15

The ultrastructure of eukaryotic cells and the functions of the different cellular components; mitochondria

Answer 15

Provides energy for the cell. High populations of mitochondria are found in the cells of organs and muscles, that are active for long periods of time, such as, the flight muscles in insects and hepatocytes (liver cells).
Contains stalked particles, where ‘energy rich’ Adenosine triphosphate, known as ATP, is made. The stalked particles preside on the inner membrane of the cristae, inside the organelle;
Site of aerobic respiration in the cell

Question 16

The ultrastructure of eukaryotic cells and the functions of the different cellular components; chloroplasts

Answer 16

Plays a critical role in photosynthesis:
The chloroplast envelope contains stroma - suspending the enzymes involved in photosynthesis.

Question 17

The ultrastructure of eukaryotic cells and the functions of the different cellular components; plasma membrane

Answer 17

A partially permeable membrane that controls the passage of all, in and out of the cell. Done in aid of its phospholipid bilayer (i.e. the fluid mosaic model).

Question 18

The ultrastructure of eukaryotic cells and the functions of the different cellular components; centrioles

Answer 18

A centrosome (a clear area of cytoplasm just outside the cell’s nucleus) contains, two centrioles. A single centriole is composed of two short bundles of microtubules, those of which are positioned perpendicular to each other.
Centrioles/centrosomes play a key role in cell division. For example, when an animal cell divides in the process of mitosis, the daughter centrosome (non-specific) migrates to the opposite pole/side of the cell, where they produce the spindle utilized in the arrangement of chromosomes, allowing homologous pairs to be arranged.

Question 19

The ultrastructure of eukaryotic cells and the functions of the different cellular components; cell wall

Answer 19

Plant cell walls contain very small cellulose fibres known as microfibrils, bound together by polysaccharides.
Provides vital structural support for the cell, allowing it to expand in cases where hydrostatic pressure is increased - making the cell turgid i.e. osmosis.
Provides mechanical support, with thanks to the strong cellulose microfibrils.
Permeable to water and other solutes.

Question 20

The ultrastructure of eukaryotic cells and the functions of the different cellular components; flagella

Answer 20

Structure based of microtubule-rings found singularly. Seen often unicellular organisms.
They grant controlled cell movement.

Question 21

The ultrastructure of eukaryotic cells and the functions of the different cellular components; cilia

Answer 21

Structure based of short microtubule rings found in relatively large populations.
Enable the movement of a material. For example, they line the trachea as a layer of specialised cells – called the ciliated epithelium – which, “waft” mucus up the trachea and into the esophagus - away from the lungs preventing possible respiratory infections.

Question 22

Photomicrographs of cellular components in a range of eukaryotic cells

Answer 22

Nucleus: large organelle
Nucleolus: dense, spherical structure inside nucleus
Nuclear envelope: surrounds the nucleus
Rough and smooth endoplasmic reticulum (ER): continuous with the nuclear envelope. RER is studded with ribosomes, SER is not.
Golgi apparatus: stack of membrane-bound flattened sacs Ribosomes, Tiny. Some are in the cytoplasm and some are bound to the RER
Mitochondria: spherical or sausage shaped. Double membrane.
Lysosomes: spherical sacs. Single membrane.
Chloroplasts, Only in plant cells. Two membranes. Contain Thylakoids.
Plasma (cell surface) membrane: phospholipid bilayer
Centrioles: small tubes of protein fibers. Pair of them next to nucleus in animal cells.
Flagella and cilia: Hair-like extensions projecting from the surface of a cell.

Question 23

The interrelationship between the organelles involved in the production and secretion of proteins

Answer 23

A strand mRNA, is made in the nucleus for it to be secreted through the pores in the nuclear envelope.

The mRNA attaches onto a ribosome on the surface of the rough endoplasmic reticulum.

The ribosome reads it, processes the mRNA into chains of amino-acids, then packages the contents into a vesicle, where it’s transported to the Golgi body.

The vesicle then fuses with the Golgi body, its contents are processed, assembled and modified (e.g. adds a carbohydrate/sugar molecule when making insulin), for the protein to be packaged into a vesicle again.

The vesicle then travels to the plasma membrane - fuses with the membrane and its contents are released outside of the cell via exocytosis

Question 24

The importance of the cytoskeleton

Answer 24

The cytoplasm contains a network of two kinds of proteins fibres which keep the cell’s shape stable by providing an internal framework. The types of protein fibres are:
Microfilaments (small solid strands made of actin, 7nm diameter) - they work in harmony with the microtubules, suspending them.
It provides an internal framework that supports the cell.
Microtubules (protein cylinders made of tubulin molecules, 25nm diameter) - provide the basis of the supporting scaffolding.
Organises and allows organelle movement. Microtubules do not move, but they provide an anchor for protein to move along with the help of motor enzymes (myosins, kinesins, dyneins).
Moves the cell in its entirety.
Construct spindle used in cell division (to enable chromosome movement within the cell)
Provides the components for cilia and flagella formation (made from a cylinder containing 9 microtubules)
Cytoskeleton needs ATP for movement.

Question 25

The similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells

Answer 25

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