Cell structure

Question 1

define the term magnification

Answer 1

magnification describes how much bigger an image appears compared with the original object.

Question 2

define the term resolution

Answer 2

resolution is the ability of an optical instrument to see or produce an image that shows fine detail clearly .

Question 3

what are the advantages of using an optical microscope

Answer 3

-cheap
-easy to use
-portable and to be used in fields as well as labs
Able to study whole large specimens

Question 4

what is the maximum magnification of an optical microscope

Answer 4

x1500, or in some cases up to x2000

Question 5

what is the calculation of magnification

Answer 5

total magnification= magnifying power of the objective lens x magnifying power of the eyepiece lens

Question 6

what is the wavelength of visible visible light and what does it means in terms of the resolution maximum

Answer 6

the wavelength of visible light ranges from 400 to 700nm so structures closer than 200nm will appear as one object (resolution is above 200nm)

Question 7

what do you call a photograph of an optical microscope view

Answer 7

photomicrograph

Question 8

how does the laser scanning microscope work

Answer 8

laser scanning microscopes are also called confocal microscopes
- they use laser light to scan an object point by point and assemble, by computer, the pixel information into one image displayed on a computer screen.
-the images are high resolution and show high contrast.
-these microscopes have depth selectivity and can focus on structures at different depths within a specimen. such microscopy can therefore be used to clearly observe whole living specimens, as well as cells.
-they are used in the medical profession, for example, to observe fungal filaments within the cornea of the eye of a patient with a fungal corneal infection, in order to give a swift diagnosis.

Question 9

how do electron microscopes work

Answer 9

electron microscopes use a beam of fast-traveling electrons with a wavelength of about 0.004nm. this means they have much greater magnification and resolution.

the electrons are fired from a cathode and focused by magnets rather than glass magnets, onto a screen or photographic plate. fast traveling electrons have a wavelength of around 125 000 times smaller than that of the central part of the visible light spectrum. this accounts for the better resolution and magnification.

Question 10

describe the differences between the two types of electron microscopes

Answer 10

transmission electron microscopes

• the specimen has to be chemically fixed, dehydrated, and stained. the beam of electrons passes through the specimen, which is stained with metal salts. some electrons pass through and are focused onto the screen or photographic plate. the electrons form a 2D black-and-white image. when photographed this is called an electron micrograph. TEM microscopes can produce a magnification of up to 2 million x, and a new generation is being developed that can magnify up to 50 million times.

scanning electron microscopes

these were developed during the 1960s. electrons do not pass through the specimen, which is whole, but cause secondary electrons to bounce off the specimen surface and be focused onto a screen. this gives this gives a 3D image with a magnification from up to 15x up to 200,000x. the image is black and white, but computer software programs can add false colour, however, the specimen still has to be placed in a vacuum and is often coated with a fine film of metal.

Question 11

how do you observe unstained specimens

Answer 11

Many biological structures, including single celled organisms such as paramecium, are colorless and transparent. Some microscopes use light inference, rather than light absorption, in order to produce a clear image without staining. Some use a dark background against which the illuminated specimen shows up. These microscopes are particularly useful for studying living specimens.

Question 12

give 3 examples of stain types used for microscopy and what they do

Answer 12

Stains are colored chemicals that bind to molecules in or on the specimen, making the specimen easy to se. Methylene blue is an all purpose stain. Some stains bind to specific cell structures, staining each structure differently so the structure can be easily identified within a single preperation. This is called differential staining. 4 examples of this are
-acetic orcein binds to DNA and stains chromosomes a dark red
-eosin stains the cytoplasm
-Sudan red stains lipids
-iodine in potassium iodide solution stains the cellulose in plant cell walls yellow, and starch granules blue/black (these will look violet under a microscope)

Question 13

How do experts prepare permanently fixed slide

Answer 13

-dehydration of the specimen
-embedding them in wax to prevent distortion when slicing
-using a special instrument to make very thin slices called sections- these are stained and mounted in a special chemical to preserve them

Question 14

What is the magnification equation

Answer 14

Magnification = image size/ actual size

Question 15

Outline the properties (organelles) of eukaryotic cells

Answer 15

All animal, protoctist, plant and fungal cells are eukaryotic. This means they all have:
-a nucleus surrounded by a nuclear envelope and containing DNA organized and wound into linear chromosomes
-an area inside the nucleus called the nucleolus, containing RNA, where chromosomes unwind; the nucleolus is involved in production of ribosomes.
-jelly like cytoplasm in which organelles are suspended
-a cytoskeleton- a network of protein filaments (actin or microtubules) within the cytoplasm that move organelles from place to place inside cells.
-a plasma membrane (cell surface membrane)
-membrane bound organelles, other than the nucleus, such as mitochondria, the Golgi apparatus and endoplasmic reticulum
-small vesicles
-ribosomes, which are organelles without membranes, where proteins are assembled.

Question 16

What does the term, membrane bound organelle actually mean?

Answer 16

This means that the organelle is covered by a membrane (similar in structure to the plasma membrane) this keeps each organelle separate from the rest of the cell, so that it is a discrete part. Prokaryotic cells do not have membrane bound organelles, allowing the to differ from eukaryotic cells.

Question 17

What is the structure and function of the organelle: nucleus

Answer 17

STRUCTURE
The nucleus is surrounded by a double membrane, called the nuclear envelope. There are pores in the nuclear envelope. However the nucleolus doesn’t have a membrane around it. This part of the organelle contains RNA (ribosomal nucleic acid).
Chromatin is the genetic material, consisting of DNA wound around histone proteins. When the cell is not dividing, chromatin is spread out or extended. And when the cell is about to divide, chromatin condenses and coils tightly into chromosomes.
FUNCTION
The nuclear envelopes function is to separate to contents of the nucleus from the rest of the cell. In some regions the inner and outer envelope fuse together. At these points some dissolved substances and ribosomes can pass through. These pores enable for a large substances, such as MRNA to leave the nucleus and sometimes steroid hormones. The nucleolus makes ribosomes (synthesize) and chromosomes within the organelle contain the organisms genes. The nucleus also provides information for protein synthesis.

Question 18

What is the structure and function of the organelle: Rough endoplasmic reticulum (RER)

Answer 18

STRUCTURE
This is a system of membranes, containing fluid filled cavities (cisternae) that are continuous with the nucleus membrane. The system is also coated with ribosomes used in protein synthesis.
FUNCTION
RER is the intracellular transport system, it forms channels for transporting substances from one area of the cell to another. It provides a large surface area for ribosomes, which assemble amino acids into proteins. These proteins then actively pass through the membrane into the cisternae and are transported to the Golgi apparatus (for modification and packaging)

Question 19

What is the structure and function of the organelle: smooth endoplasmic reticulum (SER)

Answer 19

STRUCTURE
This is a system of membranes, containing fluid filled cavities called cisternae that are continuous with the nuclear membrane. There are no ribosomes on its surface as its function is different
FUNCTION
SER contains enzymes that catalyse reactions involved with lipid metabolism, such as
-synthesis of cholesterol
-synthesis of lipids/phospholipds
-synthesis of steroid hormones
It is involved with absorbsion, synthesis and transport of lipids (from the gut)

Question 20

What is the structure and function of the organelle: Golgi apparatus

Answer 20

STRUCTURE
This consistes of a sack of membrane-bound flattened sacs. Secretory vesicles bring materials to and from the Golgi apparatus.
FUNCTION
Proteins are modified for example by-
Adding sugar to make glycoproteins
Adding lipid molecules to make lipoproteins
And being folded into their 3D shape.
The proteins are the packaged into vesicles that are pinched of and then are stored in the cell or moved to the plasma membrane, either to be incorporated into the plasma membrane, or exported out of the cell.

Question 21

What is the structure and function of the organelle: mitochondria

Answer 21

STRUCTUREThese may be spherical, rod shaped or branched,and are 2-5 micro-meters long. They are surrounded by two membranes with a fluid filled space between them. The inner membrane is highly folded into Cristae. And the inner part of the mitochondrion is a fluid filled matrix.
FUNCTION
Mitochondria are the site of ATP production during aerobic respiration. They are self replicating so that more can be made if cells energy demands increase. They are abundant within cells with much metabolic activity. For example in liver cells or at synapses of neurons.

Question 22

What is the structure and function of the organelle: chloroplasts

Answer 22

STRUCTURE
These are large organelles, around 4-10 micro-meters long. They are found in plants and some protoctists and are surrounded by a double membrane or envelope. The inner membrane is continuous with stacks of flattened membranes sacs called thylakoids which each contain chlorophyll. Each stack is called a granular. And the fluid filled matrix is called the stroma

Chloroplasts contain loops of DNA and starch grains.
FUNCTION
Chloroplasts are the site of photosynthesis. The first stage of photosynthesis, when light is trapped by chlorophyll and used to make ATP, occurs in the grana (thylakoids). Water is also split into hydrogen ions here.
The second stage, when hydrogen reduces carbon dioxide, using energy from ATP, to make carbohydrates, this occurs in the stroma. Chloroplasts are abundant in leaf cells. Particularly in the palisade mesophyll layer.

Question 23

What is the structure and function of the organelle: vacuole

Answer 23

STRUCTURE
The vacuole is surrounded by a membrane called a tonoplast, and it contains fluid.
FUNCTION
-only plant cells have a large permanent vacuole. It is filled with water and solutes and maintains cells stability, because when it pushes against the cell wall, it makes the cell turgid. If the plant cells are turned this helps support the plant in non woody plants.

Question 24

What is the structure and function of the organelle: lysosome

Answer 24

STRUCTURE
These are small bags, formed by the Golgi apparatus. Each is surrounded by a single membrane. They contain powerful hydrolytic enzymes and are abundant in phagocytic cells such as neutrophils and macrophages. They can ingest and digest invading pathogens such as bacteria.
FUNCTION
Lysosomes keep the powerful hydrolytic enzymes separate from the rest of the cell. They can also engulf old cell organelles and foreign matter, digest them and relearn the digested components to the cell for reuse.

Question 25

What is the structure and function of the organelle: cilia and undulipodia

Answer 25

STRUCTURE
These are protrusions from the cell and are surrounded by the cell surface or plasma membrane. Each contains microtubules and are formed from centrioles.
FUNCTION
The epithelial cells lining your airways each have hundreds of cillia that beat and move the band of mucus.
Nearly all cell types in the body have one cilium that acts as an antenna. It contains receptors and it allows cells to detect signals about its immediate environment.
Undulipodium enables spermatozoon to move. (Only animal cell to have undulipodium)

Question 26

What is the structure and function of the organelle : ribosome

Answer 26

STRUCTURE
Small spherical organelles, around 20 nano meters in diameter made of ribosomal RNA
Made in the nucleolus, as two sperate subunits, which pass through the N envelope and combine in the cytoplasm.
Some remain free and some combine to the rough endoplasmic reticulum
FUNCTION
Ribosomes bound to the RER are mainly for synthesizing proteins that will be exported out of the cell by exocytosis. Ribosomes that are free in the cytoplasm, either singly or in clusters, are primarily used for proteins within the cell (synthesis)

Question 27

What is the structure and function of the organelle pair: centrioles

Answer 27

STRUCTURE
The centrioles consist of two bundles of microtubules at right angles to each other, the microtubules are made of tubular protein subunits, and are arranged to form a cylinder
FUNCTION
Before a cell divides, the spindle, made of threads of tubulin forms from the centrioles. (Involved with mitosis and meiosis) - MOTOR PROTEINS USE THE TUBULIN THREADS TO WALK ALONG AND PULL CHROMOSOMES
Centrioles are also used in the formation of cilia and undulipodia
-before cilia form, the centrioles multiply and line up beneath the cell surface membrane. Microtubules then sprout outwards from each centrioles forming the cilia or undulipodia.

Question 28

What is the structure and function of the cell component: cytoskeleton

Answer 28

STRUCTURE
A network of protein structures within the cytoplasm. It consistes of:
-rod like micro filaments made of the subunits of the protein actin; they are polymers of actin and each microfillament is around 7 nm in diameter
-intermediate filaments about 10nm in diameter
-straight, cylindrical microtubules, made of protein subunits called tubulin , these are around 18 to 30 nm in diameter. The motor proteins, myosin’s, kinesics, and dyneins, are molecular motors, they are also enzymes that have a binding site that allows the hydrolysis of ATP for their energy source.
FUNCTION
The proteins microfillaments within they cytoplasm give support and mechanical strength, keep the cells shape stable and allow cell movement
Microtubules also provide shape and support to cells, and help substances and organelles to move round the cytoplasm.
Intermediate filaments also anchor the nucleus within the cell and extend between cells in some tissues, between special junctions, enabling cell-cell signaling.

Question 29

What is the structure and function of the cellulose cell wall

Answer 29

STRUCTURE
The cell wall of plants is on the outside of the plasma membrane and it is made from bundles of cellulose fibres that cross hatch.
FUNCTION
Absent from animal cells.the wall is strong and prevents plants cells bursting when turgid. It provides strength and support maintains shape and its permeable to allow some substances through.

Question 30

What are fungi cell walls made out of

Answer 30

Chitin

Question 31

Describe the process of making and secreting a protein out of a cell

Answer 31

The gene that has the coded instructions for a protein such as insulin, housed on chromatin in the nucleus, is transcribed into a length of RNA, called MRNA
Many copies of this mRNA are made and they pass out of the pores in the nuclear envelope and into the cytoplasm where they meet a ribosome
At the ribosome, the instructions are translated and insulin molecules are assembled
The insulin molecule pass into the cisternae of the RER and along the hollow sacs
Vesicles with insulin inside are pinched of from the RER and pass via microtubules and motor proteins to the Golgi apparatus.
The vesicles fuse with the Golgi apparatus, where the insulin protein molecules may be modified for release.
Inside vesicles pinched off from the Golgi apparatus, these molecules pass to the plasma membrane where they fuse with it and exit the cell by exocytosis.

Question 32

Compare the organelle structure between prokaryotic and eukaryotic cells

Answer 32

How are prokaryotic cell similar to eukaryotic cells-
-have a:
-plasma membrane
-cytoplasm
-ribosomes
-DNA and RNA
However they are different in the was that they are:
-smaller
-have much less well developed cytoskeletons with no centrioles
-dont have a nucleus
-do not have membrane bound organelles
-have a peptidoglycan cell wall
-smaller ribosomes
-have naked ringed DNA that is not wound around histone proteins and floats free within the cytoplasm.

Question 33

What is the cell division called in prokaryotic cells

Answer 33

Binary fission.

Question 34

Describe what endosymbiont theory is

Answer 34

The endosymbiotic theory states that bacterial cells were engulfed by a larger cell during evolution. The bacteria and host cell formed a beneficial symbiotic relationship. The bacterial cell became incorporated into the larger cell to become organelles. For example this is shown within chloroplasts and mitochondria due to their own ringed DNA and mitochondria’s ability to divide by binary fission.