Chapter 2- Membranes and Cell Organelles

Question 1

Cell theory

Answer 1

 All cells arise from pre-existing cells
 Cells are the basic functional unit of life
 All living things are composed of cells and the products of cells
o Cells –> tissue –> organ –> organ system –> organism

Question 2

Cell

Answer 2

• Largely filled with water
• Separated from external water by an insoluble membrane
• Need to:
  o Remove wastes
  o Produce energy for chemical reactions
  o Take in nutrients for REACTIONS
  o Export useful items
  o Grow + reproduce
• Cells are limited by their size, and they divide when too big
  o They need to be small to maintain large SA:V
  o Increasing SA:V- staying small, highly folded inner membrane
• All cells have cytosol, DNA, ribosomes, and a plasma membrane

Question 3

Prokaryotes

Answer 3

• No membrane bound organelles BC cell is too small
• Have one chromosome which is circular
• Do have a cell wall

Question 4

Eukaryotes

Answer 4

• Have many chromosomes which are linear

Question 5

Plasmids

Answer 5

• Small rings of double stranded DNA

- They have much less DNA chromosomes

Question 6

Apoptosis

Answer 6

 Programmed cell death
 Generally balanced by cell reproduction (in fully formed tissue)
 Unbalance leads to:
o An increase in cells –> tumour develops –> cancer
o A decrease in cells –> degeneration
 Caused by:
o Mitochondrial pathway (inside the cell)
 When: serious damage occurs inside the cells or a virus
 What: proteins break down mitochondrial membrane, which then causes apoptosis
o Death receptor pathway (outside the cell)
 When: not fully developed, excess cells, no longer needed
 What: cell shrinks, gets broken down whilst parts are preserved, and then broken down or recycled

Question 7

Staining

Answer 7

 Helps identify positions of regulator proteins within cells
o These proteins determines whether a cell lives or dies

Question 8

Necrosis

Answer 8

 Uncontrolled cell death
 Occurs if cell has suffered chemical or mechanical trauma, which results in damage to the plasma membrane
 Death is messy and affects surrounding cells

Question 9

Cytoplasm

Answer 9

 Cytoplasm = cytosol + all organelles except the nucleus

Question 10

Protoplasm

Answer 10

 Protoplasm = cytosol + all organelles

Question 11

Plasma membrane

Answer 11

 Present: all cells
 Function: controls the entry of dissolved substances into and out of the cell
 Structure:
o Pliable
o Phospholipid bilayer with protruding proteins + glycoproteins
 Some of these proteins form channels that allow for passive and active transport (fluid mosaic model)
 Is a bilayer because the hydrophobic lipid must associate with a lipid, and can’t associate with water
 The phospholipids are not bound (not a polymer)
o Semipermeable/partially permeable/differentially or selectively permeable
o Has cholesterol throughout it, which adds flexibility

Question 12

Glycoprotein

Answer 12

 Any naturally occurring compound where carbohydrate side chains are bonded to protein
 E.g. certain enzymes and hormones, and various antigens (on plasma membrane)

Question 13

Antigens

Answer 13

 Location: outer surface of plasma membrane
 Function:
o Recognises ‘self’ and ‘non-self’/’foreign’ cells
o Important defence mechanism against bacterial infection
 Structure:
o Protein combined with carbohydrate
o Differs between organisms (even of the same species)

Question 14

Diffusion

Answer 14

 Definition: The passive net movement of a substance from and area of high concentration to an area of low concentration
 Substances: small hydrophobic molecules (e.g. O2, CO2, steroids) + small uncharged hydrophilic molecules (alcohol, urea)
 Involves: phospholipid bilayer

Question 15

Hydrophilic

Answer 15

 Polar = water soluble = lipid insoluble = associates with water

Question 16

Hydrophobic/lipophilic

Answer 16

 Non-polar = water insoluble = lipid soluble = associates with lipids
 Can cross plasma membrane easily

Question 17

Facilitated diffusion

Answer 17

 Definition: The passive net movement of a substance from and area of high concentration to an area of low concentration. Occurs only through specific protein channels embedded in the membrane
 Substances: large, uncharged, hydrophilic molecules (e.g. glucose) + ions (e.g. salts)
 Involves: specific protein channels

Question 18

Osmosis

Answer 18

• Definition: When water moves through a semipermeable membrane from a low solute solution (high concentration of water) to a high solute solution (low concentration of water). No energy is required.
• Other terms relating to osmosis:
  o Isotonic: two solutions of the same concentration of solutes t/f no overall/net movement of water (water will still move, but at an even rate)
  o Hypotonic: lower solute solution t/f has a high concentration of water molecules. The cell would burst if it was an animal cell, or become turgid if it was a plant cell (vacuole is full) as they have cell walls preventing the bursting
  o Hypertonic: higher solute solution t/f lower concentration of water molecules. An animal cell would shrink or crenate. A plant cell would be plasmolysed or flaccid.
• Substances: water
• Involves: phospholipid bilayer

Question 19

Active transport

Answer 19

 Definition: The net movement of substances from an area of low concentration to an area of high concentration. Requires energy in the form of ATP and specific protein channels
 Substances: large, uncharged, hydrophilic molecules (e.g. glucose) + ions (e.g. salts)
 Involves: specific protein channels

Question 20

Bulk transport

Answer 20

 Definition: For the movement of very large materials in bulk
 Endocytosis:
o Bulk transport of material into a cell
 Phagocytosis: solid material
 Pinocytosis: liquid material
o Part of plasma membrane engulfs particles, forming a vesicle, which is then carried into cell
 Exocytosis:
o Bulk transport of material out of a cell
o Vesicle within cytosol fuses with the plasma membrane, and vesicle contents are released out of the cell
 Substances: protein hormones being released from a cell

Question 21

Cell wall

Answer 21

 Present: plants, fungi, and bacteria
 Function:
o Gives strength and rigidity
o Maintains shape of cell
 Structure:
o Primary cell wall: made of cellulose (plants), chitin (fungi)
o Secondary cell wall: made with the addition of lignin in some flowering plants, and adds elastic strength + support

Question 22

Nucleus

Answer 22

 Present: all eukaryotic cells
 Function:
o Control centre
o Contains the genetic instructions for the production of proteins
 Structure:
o Enclosed within the nuclear envelope (double membrane with pores)
o Has DNA dispersed throughout, which then become visible chromosomes during cell reproduction

Question 23

Nucleolus

Answer 23

 Location: within the nucleus

 Synthesises + contains RNA

Question 24

Adenosine triphosphate (ATP)

Answer 24

 Compound in which useable energy (for cells) is chemically present
 Is constantly being used up and must be replaced
 Produced during cellular respiration

Question 25

Mitochondria

Answer 25

	Present: all eukaryotic cells
	Function:
o	To produce ATP by aerobic respiration
o	Powerhouse of the cell
	Structure: outer membrane + highly folded inner membrane (where ATP is produced)

Question 26

Ribosomes

Answer 26

 Present: all cells
 Function:
o Site of protein synthesis
o Examples of protein synthesis:
 Human red blood cells- make haemoglobin (oxygen-transporting protein)
 Pancreas cells- make insulin (hormone, small protein)
 Muscle cells- make actin + myosin (contractile proteins)
 Structure:
o Not membrane-bound
o Can be attached to rough endoplasmic reticulum or free in cytosol
o Composed of rRNA and protein

Question 27

Endoplasmic reticulum

Answer 27

	Present: eukaryotes
	Function:
o	Synthesise proteins
o	Transport materials within the cell
	Structure:
o	System of channels (channel walls are formed by membranes)

Question 28

Golgi apparatus

Answer 28

 Present: eukaryotes (prominent in cells that export proteins)
 Function:
o Package + modify proteins for export

Question 29

Lysosomes

Answer 29

 Present: animal cells
 Function:
o Destroy unwanted cell parts or damaged molecules inside or outside the cell by producing digestive enzymes
o Can be involved in apoptosis (e.g. removing zones of cells of embryonic human hands)
 Structure:
o Sac-like structures
o Filled with fluid containing dissolved digestive enzymes
o Part of the cytoplasm

Question 30

Peroxisomes

Answer 30

 Present: animal and plant cells
 Function:
o Prevent the accumulation of hydrogen peroxide (poisonous in excess)
o Detoxify various toxic materials in the bloodstream
 Structure: contain the enzymes catalase and oxidase

Question 31

Endosomes

Answer 31

 Present: animal cells
 Function: pass material (that has entered the cell through endocytosis) to lysosomes for digestion
 Structure: membrane-bound

Question 32

Chloroplasts

Answer 32

 Present: plants, protists
 Function:
o Convert light energy –> chemical energy
o Anabolic
o Site of photosynthesis
 Structure:
o Double membrane (inner + outer)
o Inner membrane contains:
 Thylakoid/lamella membranous sacs, and several of these form grana, which is where chlorophyll is located. Light dependant stage
 Stroma, semi-fluid substance between grana, contains enzymes needed for light independent stage

Question 33

Cytoskeleton

Answer 33

 Present: all cells
 Function:
o Maintaining the shape of a cell
o Used as a support structure for the organelles within a cell
o Movement of materials within a cell
o If needed, movement of the actual cell
 Comprised of:
o Microtubules: hollow; made of sub-units of tubulin protein
o Microfilaments: solid, thinner, more flexible than above; made of actin
o Intermediate filaments: very tough; made of variety of proteins; tie into cytoskeleton of other cells

Question 34

Occluding junctions/tight junctions

Answer 34

 Present: animal cells
 Function:
o TOF: Tight/Occluding prevention of Fluid transfer
o E.g. preventing fluid moving from your digestive system into your body
 Not in plants because plants have pectin (sticky) to keep cells together

Question 35

Anchoring junctions/desmosomes

Answer 35

	Present: animal cells
	Function:
o	Keep cells together
o	E.g. heart muscle cells, skin cells
	Not in plants because plants have pectin (sticky) to keep cells together

Question 36

Gap junctions/communicating junctions

Answer 36

 Present: animal cells
 Function:
o Allows cells to communicate without having to go through proteins (through channels)
o Allows substances through
o Allows molecules + ions to pass through

Question 37

Scientific method

Answer 37

• Hypothesis:
  o A cause (independent variable) + effect (dependent variable)
  o Use: “That/if ‘x’ is increased/decreased, then ‘y’ will happen/increase/decrease”
  o E.g. That light exposure will increase the rate of O2 bubbles produced (indicating increased rate of photosynthesis)
• Aim:
  o Use: “To investigate the effect of…” OR “To investigate whether…”
• Control + experimental group: one without IV, one with. Needed for comparison to measure effect of IV
• Sample size: 20-100 individuals in each group
• Controlled variables:
  o Use: at least 2 factors that must be kept the same that are specific and different to those used in the questions
  o E.g. same species, temperature, amount of water, same age, etc.
• State DV
• Expected results:
  o Can include diagrams
  o Use: “Hypothesis would be supported/rejected if…”
• Experiments should be REPEATED to increase amount of data + increase validity of conclusions
• In questions do: IV, SS, CV, DV, Repeat experiment

Question 38

How are organelles beneficial?

Answer 38

• Large SA:V (highly folded inner membranes) t/f adequate quantities of substances can enter + leave cell
• Different chemical reactions can happen at the same time without interference

Question 39

What is the order of cell structures of their use in protein synthesis?

Answer 39

• Nucleus –> rough endoplasmic reticulum –> Golgi body –> vesicles

Question 40

Chromatin

Answer 40

• Unwound chromosomes

- Loose DNA with protein