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AQA AS BIOLOGY 2015+ > 2 Cell structure > Flashcards

2 Cell structure Flashcards

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1
Q

Methods of studying cells

A

Cells are not visible to the naked eye so microscopes are used to produce a magnified image of an object.The material placed under the microscope is the object and the appearance viewed under the microscope is the image.

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2
Q

Magnification Calculations

A

Magnification of an object is how many times bigger the image is when compared to the object.Use the formula magnification= Image size/actual size
(Remember to ensure the units are the same for both the image and the object.)

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3
Q

Resolution

A

Resolution is defined as how well you can distinguish between two points. Greater resolution means greater clarity, so the image produced is clearer and more precise.

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4
Q

How does Light Microscopes work?

A

Light from the mirror is reflected up through the specimen (object) into the powerful objective lens which produces the first magnification.Image produced by the lens is then magnified again by the eyepiece lens (magnifying glass).

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5
Q

What are the disadvantages of light microscopes?

A
  • Long wavelength of light means light microscopes have a poor resolution. Can only distinguish between 2 objects if they are 0.2μm away.
  • Low magnification (Max magnification- x 1500)
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6
Q

What are the advantages of light microscopes?

A
  • Easy to use - Cheap to purchase - Shows true colours of the specimen - Can view live specimens
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7
Q

How does a Transmission Electron Microscope work?

A

A beam of electrons is focused on the thin specimen by a condenser electromagnet. Some parts of the specimen absorb the electrons thus appear darker and other parts allow the electrons to pass through so appear bright. The image produced on the screen is photographed to produce a photomicrograph.

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8
Q

Disadvantages of TEM

A
  • May contain artefacts which distorts the real image
  • Whole system is carried in a vacuum (so electrons don’t interact with air molecules) but this means live specimens can’t be viewed - Complex staining process
  • Doesn’t show true colours of the specimen - Very expensive
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9
Q

Advantages of TEM

A
  • High resolution (beam is focused by an electromagnet) (Max resolution: 0.1 nm)
  • High Magnification (Max magnification : X 500000)
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10
Q

How does a Scanning Electron Microscope work?

A

A beam of electrons is directed onto the surface of a thin specimen. The beam passes back and forth across a section of a specimen in a regular pattern. The electrons are then spread based on the outlines of the specimen surface. Finally, a 3D image is created based on the computer analysis of the pattern of scattered electrons.

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11
Q

Disadvantages of SEM

A
  • Very expensive - Sample needs to be extremely thin -Shows false colour - Extensive training required to use an SEM - Live specimens can’t be viewed
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12
Q

Advantages of SEM

A
  • High resolution (Max- 20 nm)

- High magnification (Max- x 100000)

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13
Q

Before Cell Fractionation, why is the sample placed in a cold, buffered isotonic solution?

A
  • Cold: To reduce/ prevent enzyme activity that might break down the organelle
  • Buffered: Maintains the same PH as a change to the PH could alter the structure and function of the organelle
  • Isotonic: Prevents organelles from bursting or shrinking due to an osmotic gain or loss of water
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14
Q

What is the first stage of cell fractionation?

A

Homogenisation - Cells are broken up by a homegenizor (blender) releasing organelles from the cell. The homogenate is then filtered to remove any cells/large pieces of debris.

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15
Q

What is the final stage of cell fractionation?

A

Ultracentrifugation- Fragments in the filtered homogenate are separated using a centrifuge. The heaviest organelle falls to the bottom and the rest remains as a fluid at the top called supernatant. The supernatant is removed and placed in another tube and spun at a higher speed. The next heaviest organelle is forced to the bottom.

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16
Q

Spinning at different speeds means you separate the less and more dense organelles. What is the order of density of organelles? Starting with the most dense.

A

Nuclei, Mitochondria, Chloroplasts , Endoplasmic Reticulum, Golgi apparatus and Ribosomes.

A mnemonic to help (Naughty Musfira Can Even Gobble Rats) ; p

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17
Q

What is a Tissue?

A

Collection of similar cells that perform a specific function

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18
Q

What is an Organ?

A

A combination of coordinated tissues that perform a variety of functions and often have a predominant function.

19
Q

What is an Organ System?

A

Organs work together as a single unit known as an organ system. Organs are grouped together to perform functions more effectively.

20
Q

What is the role of the Nucleus?

A
  • Nucleus contains the organisms hereditary units and controls all the activities of the cell.
21
Q

What does the Nucleus Contain?

A
  • Nuclear envelope: A double membrane that controls the exit and entry of materials and contains the reactions taking place within it.
  • Nucleolus: Manufactures ribosomal RNA and assembles the ribosomes.
  • Nucleoplasm: jelly like materiel which makes up most of the nucleus.
  • Nuclear pores: Allows passage of large molecules e.g. MRNA out of the nucleus.
22
Q

Ribosome

A
  • Site for protein synthesis - Contains a large and small sub unit - Ribosomes are smaller in prokaryotic cells (70s) than eukaryotic cells (80s)
23
Q

What is the role of the Mitochondria?

A

Site of Aerobic respiration, so is responsible for the production of ATP from respiratory substrates to release energy.

24
Q

What are the structures of the Mitochondria?

A
  • Outer and inner membrane (double membrane): controls the the entry and exit of material
  • Cristae: Provides a large surface area for the attachment of enzymes and other proteins involved in respiration.
  • Matrix: contains proteins, lipids, ribosomes and DNA to allow mitochondria to produce its own proteins. Contains enzymes involved in respiration too.
25
Q

Chloroplast

A
  • Chloroplast envelope: Double plasma membrane which is highly selective in what it allows to enter and leave the chloroplast.
  • Grana- (stacks of thylakoids) contains chlorophyll which absorbs sunlight for photosynthesis
  • Contains both DNA and ribsomes thus can quickly and easily manufacture proteins needed for photosynthesis.
  • Stroma- ( where LIR occurs) responsible for synthesis of sugars (contains starch grains)
26
Q

Rough Endoplasmic Reticulum

A
  • Has ribsomes on its outer surface

- Provides a large surface for the synthesis of proteins and glycoproteins.

27
Q

Smooth Endoplasmic Reticulum

A

No ribosomes

- Synthesises, stores and transports lipids and carbohydrates

28
Q

Which Polysaccharide is the cell wall of eukaryotic cells made from?

A

Cellulose- provides strength in order to prevent it the cell from bursting under the pressure created by an osmotic entry of water

29
Q

Vacuoles

A

Fluid filled sac surrounded by a membrane tonoplast

  • Contains cell sap ( solution of mineral salts, sugars, amino acids, wastes and pigments.)
  • Sugars and Amino Acids act as a temporary food store.
30
Q

Golgi Apparatus

A
  • Processes, packages and sometimes modifies new proteins and lipids
31
Q

Golgi Vesicle

A
  • Stores the lipids and proteins and transports them to the cell surface membrane - Fuses with the membrane and releases its contents outside.
32
Q

Lysosomes

A

Contains Lysozyme- hydrolyses materiel ingested by phagocytic cells - Digests worn out organelles
- Completely breaks down cells after they have died (Autolysis)

33
Q

Prokaryotic Cells

A
  • Smaller than Eukaryotic cells
  • Cell wall is made from muerin -Slimy capsule (form of protection) makes it harder to catch and allows groups of bacteria to stick together - Free laying genetic material ( contains information for the replication of bacteria cells) - Plasmids: allows independent reproduction and resistance to harmful chemicals - Flagella: rotates to allow movement away from harmful substances and towards nutrients
34
Q

What are differences between prokaryotic and eukaryotic cells?

A
  • Instead of Mitochondria Prokaryotic cells contains Mesosomes which provides a large surface area for the attachment of enzymes involved in respiration.
  • Prokaryotic cells don’t have a nucleus
  • DNA in eukaryotic cells is associated with proteins called histones
35
Q

Mitosis

A
  • Cell reproduces itself to form two identical daughter cells with the same number of chromosomes as the parent cell - It important for growth and repair of cells and Asexual reproduction.
36
Q

Interphase

A

Interphase is before Mitosis. The cell grows and increases its sub-cellular structures and duplicates its DNA.

37
Q

What are the Stages of Mitosis?

A

Prophase- Chromosomes shorten and thicken and the nucleolus disappears and nuclear envelope breaks down.

  • Metaphase- Chromosomes arrange themselves at the equator of the cell.
  • Anaphase- Chromatids are pulled by spindle fibres to opposite poles of the cell.
  • Telophase - Chromosomes become longer and thinner until they become chromatin - spindle fibres disintegrate and nuclear envelope and nucleolus re-form.
38
Q

Cytokineses

A

Cytoplasm and cell membrane divides during cytokineses forming 2 new identical daughter cells.

39
Q

Binary Fission (cell division in Prokaryotic cells)

A
  • DNA molecule and plasmids replicate and attach to the cell surface membrane - Cell membrane grows between 2 DNA molecules dividing the cytoplasm into 2 - A new cell wall forms between the 2 DNA molecules diving the original cell into 2 new identical daughter cells.
40
Q

Do all Eukaryotic cells divide?

A

Np some Eukaryotic cells do not retain the ability to divide.

41
Q

Mitosis is a controlled process. What happens when there is uncontrollable cell division?

A

Uncontrollable cell division leads to the formation of a tumour where when it becomes invasive it becomes cancerous.

42
Q

What’s the difference between Malignant and Benign tumour?

A

Malignant Tumour - Grows rapidly, less- compact, More likely to be life threatening
Benign Tumour- Grows more slowly, more compact, less likely to lead to cancer

43
Q

Treatments of Cancer

A

Often involved disrupting cell cycle and cell division e.g Chemotherapy ( prevents DNA replication. Inhibits metaphase stage by interfering with spindle formation.)

44
Q

Why is hair loss seen in Chemotherapy patients?

A

Also disrupts the cell cycle of normal cells but cancer cells have a faster rate of division so they are affected more. Hair producing cells also have a fast rate of division so patients undergoing cancer treatment are vulnerable to hair loss.

AQA AS BIOLOGY 2015+ (10 decks)

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