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Biology A-Level > Cells > Flashcards

Cells Flashcards

1
Q

What is a eukaryotic cell?

A

They are complex and include all animal and plant cells as well as in algae.

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2
Q

Outline cell-surface membranes:

A

Structure: They are found on the surface of animal cells and inside the cell wall of plant cells. They contain lipids and proteins which are enclosed alongside it.

Function: The lipids and proteins regulate what substances enter and leave the cell and act as a barrier fr receptors such as glycolipids and glycoproteins.

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3
Q

Outline the nucleus:

A

Structure: Largest organelle, spherical in shape and contains a nuclear envelope. It is separated from the rest of the cell because it contains DNA and proteins which cannot be in harsh environments. It regulates what substances go in and out of the nucleus through nuclear pores which are found throughout nuclear envelope. Contains nucleolus.

Function: DNA contains instructions to make proteins; pores allow substances to pass through nucleus and cytoplasm and nucleolus makes ribosomes.

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4
Q

Outline mitochondria:

A

Structure: Contain double membrane. Inner membrane folded to form cristae and inside contains matrix containing enzymes involved in respiration and where ATP synthesis takes place. The cristae enables compartmentalization separating enzymes for different steps.

Function: Site of aerobic respiration and where ATP is produced.

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5
Q

Outline chloroplasts:

A

Structure; Surrounded by double membrane and inside these contain thylakoid membranes. They are stacked up in the chloroplast to form grana. Grana is linked together by lamellae.

Function; Where photosynthesis takes place and happens in the grana or stroma.

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6
Q

Outline golgi apparatus:

A

Structure: A stack of fluid sacs located near the nucleus. It makes lysosomes which are made into vesicles.

Function: Processes and packages new lipids and proteins to be exported out of the cell and consists of two faces CIS faces and TRANS face.

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7
Q

Outline lysosomes:

A

Structure: Have no distinct structure and type of golgi vesicle.

Function: Contains digestive enzymes called lysozyme known as hydrolytic enzymes which separate from the cytoplasm surrounding membrane and break down worn out components of the cell.

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8
Q

Outline ribosomes:

A

Structure: Smallest organelle floating freely in the cytoplasm where it makes proteins for cells own use and attached to rough endoplasmic reticulum where they make proteins to be exported out of the cell. Contain two subunits.

Function: Site where proteins are made and the units come together when involved for protein synthesis and aren’t surrounded by membranes.

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9
Q

Structure of rough endoplasmic reticulum:

A

Structure: Covered with ribosomes which are responsible for making proteins to be exported outside of cell membranes.

Function: Folds and processes proteins that have been made at the ribosomes and are then sent to the golgi apparatus.

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10
Q

Structure of smooth endoplasmic reticulum:

A

Structure: Don’t contain ribosomes.

Functions: Synthesize lipids and other molecules as well as hormones for intracellular use and export which is involved in detoxification of toxins which are consumed by cells producing metabolite byproducts.

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11
Q

Structure of cell vacuole:

A

Structure: Found in the cytoplasm and surrounded by tonoplast membrane containing cell sap.

Function: Helps maintain pressure inside the cell keeping it rigid and prevents plant from wilting and is also involved in isolation of unwanted chemicals inside the cell.

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12
Q

Structure of centrioles:

A

Structure: Microtubules not surrounded by membranes.

Function: Form fibers in cell division and spindle fibers which separate chromosomes.

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13
Q

Structure of cytoplasm:

A

Structure: Fluid like substance between cell membranes and nucleus composed of water and some inorganic/organic substances.

Function: Where chemical reactions occur containing molecules such as enzymes aid metabolic activity and break down waste.

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14
Q

What are prokaryotic cells:

A
  • Cytoplasm: Lacks membrane bound organelles.
  • Smaller ribosomes.
  • No nucleus: have circular DNA molecule freely floating in cytoplasm and present as one long coiled DNA strand and not attached to any histone proteins.
  • A cell wall: contains muerin which has a glycoprotein with carbohydrate attached to it.
  • Plasmids, flagellum, capsule.
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15
Q

What are viruses?

A
  • They are nucleic acids that are non living.
  • Smaller than bacteria and don’t contain ribosomes, lysosomes and plasma membranes unlike bacteria.
  • All viruses reproduce themselves and invade inside other organisms cells; aka as host cells.
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16
Q

Structure of viruses?

A
  • In the middle is the CORE consists of genetic material DNA or RNA.
  • Protein coat around core called the capsid.
  • Attachment proteins stick out from capsid letting viruses cling onto suitable host cells.
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17
Q

Describe binary fission process:

A
  • The circular DNA and plasmids replicate- DNA loops replicate once and plasmids multiple times.
  • Cell gets bigger and DNA loops split moving to oppose ends of the cell.
  • Cytoplasm begins dividing, and cell walls reforms.
  • Cytoplasm decides forming two daughter cells containing one copy of circular DNA and variable number of copies of the plasmids.
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18
Q

Outline how viruses replicate:

A
  • They attach onto host cell with attachment proteins on surface.
  • Inject nucleic acid into host cells.
  • Viral nucleus acids then hijack cells machinery coding for metabolic processes to product viral components- nucleic acids, enzymes, structural proteins which are then assembled into new virus.
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19
Q

Define magnification & resolution:

A

Magnification- how much bigger the image is compared to specimen.

Resolution- how detailed the image is.

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20
Q

Outline optical microscopes:

A
  • They use light to form images.
  • They have a magnification of x1500
  • They have a resolution of 0.2 micrometers.
  • Unable to distinguish ribosomes, lysosomes and endoplasmic reticulum.
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21
Q

Advantages and disadvantages of optical microscope

A

+ They use live specimens.
+ Light, cheap and portable.
- Produce low resolution images.
- Cannot distinguish many organelles.

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22
Q

Outline electron microscopes:

A
  • They use electrons to form images.
  • They have a magnification of 150000.
  • They have a resolution of 0.0002 micrometers.
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23
Q

Outline transmission electron microscopes (+ / -)

A
  • They use electromagnets to focus beam of electrons which is transmitted through specimen.
  • Denser parts are where there are more electrons so appear darker in images.
    + Produce high resolution images.
  • Only uses thin specimens.
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24
Q

Outline scanning electron microscope (+ / -)

A
  • They scan beam of electrons knocking off electrons from specimen forming image.
  • They form 3D image.
    + Use thick specimens.
  • Produce lower resolution images.
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25
Q

Describe cell fractionation:

A

1) Homogenization- the cell is broken open and content and organelles are released and placed into cold, isotonic buffered solution. The plasma membrane is broken using a homogenizer.
- Cold; reduce enzyme activity.
- Isotonic; to keep same water potential as solution preventing organelles from bursting.
- Buffered; prevent pH changes.

2) Filtration- the homogensied solution is filtered through gauze separating from debris and or connective tissue
3) Ultracentrifugation- The cell fragments are the placed into tube into centrifuge and spun at a low speed. The heaviest organelle is flung to bottom forming a thick sediment called the pellet. The remaining fragments are suspended in the supernatant and drained off. The process is repeated at higher speeds and the pellet consists of lighter organelles each time.

Heaviest- Lightest: Nucleus, Chloroplast, Mitochondria, Lysosomes, Endoplasmic reticulum, Ribosomes.

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26
Q

How to make temporary mount?

A
  • Add water onto glass slide.
  • Obtain thin sections of tissue and place on slide.
  • Stain with iodine solution if testing starch grains.
  • Lower cover slip using mounted needle.
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27
Q

Outline different between mitosis and meiosis?

A

Mitosis forms 2 daughter cells, meiosis forms 4 daughter cells.
Meiosis forms genetically different cells and mitosis forms genetically identical cells.

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28
Q

Outline interphase:

A

DNA is unravelled and genetic material is doubled.

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29
Q

Outline prophase:

A
  • Chromosomes exist under microscope.
  • Nuclear envelope disintegrates.
  • DNA shortens and condenses.
  • Centrioles split moving to opposite ends of the cell forming spindle fibers.
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30
Q

Outline metaphase:

A
  • The chromosomes are visible under the microscope.
  • Nuclear envelope disintegrates.
  • DNA becomes shortened and condensed.
  • Centrioles split and form spindle fibers.
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31
Q

Outline anaphase:

A
  • Centromeres that hold 2 sister chromatids split and spindle fibers contract moving chromatids to opposite ends of the cell.
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32
Q

Outline telophase and cytokinesis:

A
  • The chromatids exist as chromosomes and are no longer visible under the microscope.
  • The nuclear envelope reappears.
  • Spindle fibres disintegrate.
  • Cytoplasm splits forming 2 daughter cells.
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33
Q

How do you observe mitosis using root tip squash?

A

1) Cut 1cm tip of growing root and it needs to be at the tip because that is where growth occurs and mitosis takes place. Place into watch glass.
2) Prepare boiling tube containing HCL and place in 60 degrees celsius waterbath.
3) Transfer the HCl into watch glass and add stain.
4) Heat mixture using hot plate and watch and heat for 5 mins making sure root tip does not dry out and most liquid should evaporate.

34
Q

Outline the stages of the cell cycle:

A
  • G1; Cell gets bigger and proteins and other organelles are produced.
  • S phase; (Synthesis) DNA replication.
  • G2- Cell keeps growing and proteins are produced for cell division.
35
Q

How to work out magnification?

A

Image size/ Actual size

36
Q

How to work out mitotic index?

A

Number of cells undergoing mitosis (PMAT)/ total number of cells in field x total time of cycle.
OR
Number of cells undergoing mitosis (PMAT)/ total number of cells in field of view x 100.

37
Q

What is cancer?

A

Uncontrolled cell divisions forming mutations which produce tumors and spread to surrounding tissues.

38
Q

Name two cancer types and differentiate between them:

A
  • Benign; Slow growing tumor, does not spread to surrounding tissues.
  • Malignant- Fast spreading tumor, spreads to surrounding tissues.
39
Q

Describe treatments for cancers:

A
  • G1- Chemotherapy will prevent enzymes from synthesizing needed for DNA replication and entering the s phase therefore disrupting the cell cycle and causing the cell to kill itself.
  • S- Radiation damages DNA and when the cell enters the s phase it is detected to see if there is damage done to the DNA and if so it is forced to kill itself preventing the spread of it to surrounding tissues.
40
Q

What are cell surface membranes?

A

They act as barrier to cells controlling which substances enter and leave the cell. They are partially permeable membranes.

41
Q

Why are CSM known as the ‘fluid mosaic model’?

A

Fluid- Because their phospholipids produced in bilayer are constantly moving.
Mosaic- Because contain many different proteins; channel and carrier proteins help move larger and charged particles across the CSM, receptor proteins detect chemical signals released form other cells, proteins and lipids also contain glycoproteins and glycolipids.

42
Q

Outline structure and function of phospholipids:

A
  • They form a bilayer.
  • Head is hydrophilic meaning it’s attracted to water.
  • Tail is hydrophobic meaning it repels from water.
  • Centre of bilayer is hydrophobic meaning water soluble substances cannot pass through. Lipid soluble substances- pass through via the phospholipid bilayer.
43
Q

Why is cholesterol found in the CSM?

A

It is found between phospholipid molecules and binds to hydrophobic tail making phospholipids move closer together. It restricts movement of phospholipids to make them less fluid and more turgid. They also maintain the shape of cells which do not have cell walls.

44
Q

Define diffusion:

A

Movement of molecules from an area of high concentration to an area of low concentration down the concentration gradient. It is a passive process meaning does not require energy.

45
Q

Compare simple diffusion and facilitated diffusion?

A
  • Simple diffusion; When molecules diffuse directly through the cell membrane.
  • Facilitated diffusion; When larger or charged molecules are unable to pass directly through csm so go through channel and carrier proteins.
  • They are both passive processes and move from high concentration to low concentration down the concentration gradient.
46
Q

Outline how carrier and channel proteins export substances;

A
  • Carrier proteins; They carry large molecules across the cell surface membrane. The molecule attaches to the protein and the protein changes shape and releases the molecule onto the opposite side of the csm.
  • Channel proteins: They carry charged particles through pores found on csm.
47
Q

Factors affecting simple & facilitated diffusion;

A

Simple diffusion:

  • Higher concentration, the faster the rate of diffusion up until equilibrium.
  • Thin; short diffusion pathway faster rate of diffusion.
  • Large surface area faster diffusion rate.

Facilitated diffusion:

  • Higher concentration, the faster the rate of diffusion up until equilibrium.
  • Number of channel and carrier proteins- the more there are the faster the rater of diffusion.
48
Q

What is osmosis?

A

Diffusion of particles from a high water potential to low water potential across partially permeable membrane. Passive process doesn’t require energy.

49
Q

Factors affecting osmosis?

A
  • High water potential means faster rate of osmosis up until equilibrium.
  • Thin, means short osmosis pathway.
  • Large surface area means faster rate of osmosis.
50
Q

Define active transport:

A

Movement of particles from area of low concentration to area of high concentration against the concentration gradient. Active process requiring ATP (hydrolysis of ATP into ADP and Pi releasing energy).

51
Q

What is the role of co-transporter proteins in active transport?

A

Co-transporter proteins are a type of carrier protein. They can bind to two molecules at one time. One molecules concentration gradient causes other molecule to go against it’s own concentration gradient.

52
Q

Factors affecting active transport?

A
  • Number of carrier proteins- the more, the faster the rate of active transport.
  • Speed of individual carrier proteins- faster they are the faster active transport is.
53
Q

Describe the absorption of sodium ions and glucose by cells lining the mammalian ileum:

A
  • Sodium ions actively transported out of the ileum epithelial cells into the blood by the sodium-potassium pump (now higher concentration of sodium ions in the lumen than inside the cell).
  • Sodium ions diffuse from lumen of ileum into epithelial cells down their concentration gradient via sodium-glucose co transporter proteins.
  • The co-transporter carried glucose into cell with sodium so glucose inside cell increases.
  • Glucose diffuses out of the cell into the blood down it’s concentration gradient by protein channel via facilitated diffusion.
54
Q

What are antigens?

A

They are found on the surface cells and generate an immune response.

55
Q

What do antigens detect?

A
  • Abnormal body cells.
  • Toxins.
  • Pathogens.
  • Cells from different individuals of same organisms.
56
Q

How do phagocytes engulf pathogens?

A
  • Phagocyte recognizes foreign antigen on pathogen.
  • The phagocytes cytoplasm engulfs the pathogen.
  • Phagocytic vacuole is formed around pathogen and lysosomes fuse with it. Lysozyme’s break down the pathogen.
  • The antigen sticks to surface and activate immune response.
57
Q

How do phagocytes activate t cells?

A
  • T cells contain receptors which bind to complementary antigens and activate their t cells. Each t cell carries out different functions. T helper cells activate phagocytic cells and cytotoxic cells and send them chemical messages to kill abnormal foreign cells. They also activate B cells which secrete antibodies.
58
Q

Describe how t cells activate b cells which divide into plasma cells:

A
  • B cells contain specific antibodies on their surface which bind to specific antigen forming antigen-antibody complexes. These alongside t helper cells activate the B cells and clonal selection occurs dividing the cells into plasma cells.
59
Q

Describe how plasma cells make more antibodies to a specific antigen:

A
  • Plasma cells are identical to b cells and they secrete antibodies for their own antigens aka as monoclonal antibodies. Form antigen antibody complexes.
  • Antibodies have two binding sites meaning they can clump together aka as agglutination.
  • Phagocytes bind to the antibodies and phagocytose many pathogens which destroys the pathogens carrying the antigen.
60
Q

What are antibodies?

A

They are proteins made up of chain of amino acids and the specificity of antibody depends on its variable regions (all have specific tertiary structures) which form binding sites complementary to specific antigens. They all have same constant region.

61
Q

Difference between cellular and humoral response?

A

Cellular- The t cells and other immune system cells that they interact with.
Humoral- B cells, clonal selection and monoclonal antibodies form the humoral response.

62
Q

Outline the primary immune response:

A
  • When antigen first enters the body it activates the immune system.
  • It is slow because there aren’t enough b cells to bind with antibodies but eventually will produce enough of right antibody to overcome infection. They will show symptoms.
  • After being exposed to antigen t cells and b cells produce memory cells which remain in body for long time (memory b cells- record specific antibodies & memory t cells- remember specific antigen). The person is now immune.
63
Q

Outline the secondary immune response:

A
  • If the same pathogen enters the body again the immune system will be stronger and quicker.
  • Clonal selection will happen faster and memory b cells will activate and divide into plasma cells. Memory t cells activated and divide into correct type of t cells to kill cell carrying antigen.
  • Gets rid of pathogen before showing symptoms.
64
Q

What are vaccines?

A

They contain antigens causing body to produce memory cells against particular pathogen without pathogens causing disease meaning you become immune without showing symptoms.

65
Q

Disadvantages of vaccines?

A
  • It could be broken down by enzymes in the gut or the molecules of the vaccines may be too large to be absorbed into the blood.
  • Tested on animals first.
  • Can have side effects.
66
Q

What is herd immunity?

A

You have to vaccinate a large enough proportion if the population in order to break the chain of transmission, providing protection for individuals who are not immune.

67
Q

What is antigenic variability?

A

It affects the production of vaccines to help prevent people catching influenza.

  • The influenza vaccine changes every year because antigens on the surface of the influenza virus forms new strains.
  • Memory cells from one strain will not recognize other strains with different antigens as they are immunological distinct.
  • New vaccines made and most effective one is chosen.
68
Q

What is active immunity?

A

When your immune system makes its own antibodies.

  • Natural; when you become immune after catching disease.
  • Artificial; when you become I’m one after being given vaccination.
69
Q

What is passive immunity?

A

When you are given antibodies made by different organism.

  • Natural; when baby become immune due to antibodies given from mother through placenta when breast fed.
  • Artificial; when you become immune after being injected with antibodies from someone else.
70
Q

3 differences between active and passive immunity?

A
  • AI requires exposure to antigens whereas PI does not.
  • In AI memory cells are produced but not in PI.
  • In AI protection is long term because antibody complementary to antigen whereas in PI protections short term because antibodies given are broken down.
71
Q

What are monoclonal antibodies?

A

They are antibodies that are made from genetically identical groups of b cells and have unique tertiary structures. They can bind to anything.

72
Q

Describe the use of monoclonal antibodies in targeting medication to specific cell types; (Cancer cells)

A

Cancer cells contain antigens called tumor markers. Monoclonal antibodies bind to tumor markers and also attach onto anti-cancer drugs. When the antibodies come into contact with cancer cells they’ll bind to tumor markers and will only accumulate specific cancer cells so therefore have low side effects.

73
Q

Describe the use of monoclonal antibodies in medical diagnosis; (Pregnancy test)

A
  • Application contains antibodies for hCG bound to a colored bead (blue).
  • Urine is applied to application and if hCG is present it’ll bind to antibodies forming antigen-antibody complexes.
  • Urine is moved up the test alongside the colored bead.
  • The test strips antibody’s are immobilized
  • If hCG is present the test strip will turn blue because immobilized antibodies bind to it.
  • If no hCG is present the colored bead will move along the test and won’t bind to anything with no color change too.
74
Q

What is the ELISA test used for?

A
  • It uses monoclonal antibodies to detect person has antibodies to certain antigens.
  • If there is a color change shows that antigen/antibody is present.
75
Q

Describe how ELISA test is used as a HIV test:

A
  • HIV antigens are attached to bottom of well. A sample of patient blood plasma is placed into well and if there any HIV- specific antibodies they’ll bind to antigens. The well is then washed out removing any unbound antibodies.
  • A secondary antibody is added with an enzyme attached and will bind to specific antibodies. The well is washed again removing any unbound antibodies.
  • A colorless substrate is added to solution. If changes color then antibodies are presenting blood and person is infected with HIV.
76
Q

Define HIV:

A

Human immunodeficiency virus affects the immune system and leads to AIDS (acquired immune deficiency syndrome).
- It kills helper T cells acting as host cells for the virus. Decrease in t helper cells creates AIDS.

77
Q

Describe the structure of HIV:

A
  • A core containing RNA and some proteins (like enzyme reverse transcriptase) which is needed for virus replication.
  • Protein coat containing capsid.
  • An extra layer called an envelope made of membrane stolen from cell membranes of host cell.
  • Sticking out from envelope are many copies of attachment proteins that help HIV attach to the host helper T cells.
78
Q

How does HIV replicate inside its host helper T cells?

A
  • The attachment protein attaches to receptor molecule on cell membrane of host helper T cell.
  • The capsid is released into the cell where it releases RNA into cells cytoplasm.
  • Inside the cells reverse transcriptase makes a complementary strand of DNA from the viral RNA template.
  • Double stranded DNA is made and inserted into human DNA.
  • Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA.
  • The viral proteins assemble into new viruses and infect other cells.
79
Q

How does HIV cause the symptoms of aids?

A
  • People with HIV have AIDS when symptoms of failing immune system of decrease of t helper cells.
    Initial symptoms of AIDS include minor infections of mucous membranes and as it progresses the number of immune system cells decreases. During late stages of AIDS patients have low number of immune system cells and can develop range of serious infections.
80
Q

Why are antibiotics ineffective against viruses?

A

Because viruses do not have internal organelles or any metabolism that can be targeted

Biology A-Level (10 decks)

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