Topic 1: Cells

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Topic 1 Cells
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1.1 Cell Theory

• 1.1.1
• Discuss the theory that living organisms are
  composed of cells. (3)
• Skeletal muscle and some fungal hyphae are not
  divided into cells but have a
  multinucleate cytoplasm. Some biologists consider
  unicellular organisms to be acellular.

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1.1 Cell Theory

• 1.1.2
• State that a virus is a non-cellular structure
  consisting of DNA or RNA surrounded by a protein
  coat. (1)

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1.1 Cell Theory
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1.1 Cell Theory

• 1.1.4
• Explain three advantages of using light
  microscopes. (3)
• Advantages include
• colour images instead of monochrome,
• a larger field of view,
• easily prepared sample material,
• the possibility of examining living material and
  observing movement.

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1.1 Cell Theory

• 1.1.5
• Outline the advantages of using electron
  microscopes. (2)
• Greater
• Resolution the ability to distinguish between
  two points on an image. Like pixels in a digital
  camera.
• Magnification how much bigger a sample appears
  to be under the microscope than it is in real
  life.

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1.1 Cell Theory

• Transmission electron microscopes pass a beam of
  electrons through the specimen. The electrons
  that pass through the specimen are detected on a
  fluorescent screen on which the image is
  displayed.
• Thin sections of specimen are needed for
  transmission electron microscopy as the electrons
  have to pass through the specimen for the image
  to be produced.

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1.1 Cell Theory

• Scanning electron microscopes pass a beam of
  electrons over the surface of the specimen in the
  form of a scanning beam.
• Electrons are reflected off the surface of the
  specimen as it has been previously coated in
  heavy metals.
• It is these reflected electron beams that are
  focused on the fluorescent screen in order to
  make up the image.
• Larger, thicker structures can thus be seen under
  the scanning electron microscope as the electrons
  do not have to pass through the sample in order
  to form the image.
• However the resolution of the scanning electron
  microscope is lower than that of the transmission
  electron microscope.

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1.1 Cell Theory
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1.1 Cell Theory

• 1.1.6
• Define organelle. (1)
• Literally little organ
• An organelle is a discrete structure within a
  cell, and has a specific function.
• i.e. nucleus, cell membrane, mitochondria

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1.1 Cell Theory

• 1.1.7
• Compare the relative sizes of molecules, cell
  membrane thickness, viruses, bacteria, organelles
  and cells, using appropriate SI units (2)
• Appreciation of relative size is required,
• molecules (1 nm),
• thickness of membranes (10 nm), xref. 1.4
• viruses (100 nm),
• bacteria (1 µm), xref. 1.33
• organelles (up to 10 µm), xref. 6.4.2, 7.1.3,
  7.2.1
• most cells (up to 100 µm).
• Dont forget all of these structures are in 3D
  space

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1.1 Cell Theory

• 1 nm 1/1,000,000,000 of a meter, or . . .
  
• 0.000000001m, or . . .
• 1 billionth of a meter
• 1 µm 1/1,000,000 of a meter, or . . .
• 0.000001m, or . . .
• 1 millionth of a meter
• 1 nm 1/1,000 of a µm, or
• 1 µm 1,000 nanometers
• Therefore. . .

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1.1 Cell Theory

• A 100 µm cell 10x larger than a. . .
• A 10 µm organelle 10x larger than a. . .
• A 1 µm bacteria 10x larger than a. . .
• A 100 nm virus 10x larger than a. . .
• A 10 nm membrane 10x larger than a. . .
• A 1 nm molecule

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1.1 Cell Theory
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1.1 Cell Theory

• 1.1.8
• Calculate linear magnification of drawings. (2)
• Drawings should show cells and cell
  ultra-structure with scale bars
• Magnification could also be stated, eg x250.

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1.1 Cell Theory

• 1.1.9
• Explain the importance of the surface area to
  volume ratio as a factor limiting cell size. (3)
• The rate of metabolism of a cell is a function of
  its massvolume ratio,
• Whereas the rate of exchange of materials and
  energy (heat) is a function of its surface area.
• Simple mathematical models involving cubes and
  the changes in the ratio that occur as the sides
  increase by one unit could be compared.

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Assume we have 3 cubes
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With sizes
2
1
1 cm
100 cm
10 cm
What will happen to ratio between V and S.A. as
their size increases?
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Ratio of VS.A.
1 cm3
6 cm2
6
600 cm2
1 000 cm3
0.6
1 000 000 cm3
60 000 cm2
0.06
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1.1 Cell Theory

• 1.1.10
• State that unicellular organisms carry out all
  the functions of life. (1)
• MOVEMENT Intracellular and/or extracellular
• RESPIRATION Gas exchange. Not always O2 and
  CO2
• NUTRITION Need raw materials, i.e.- food,
  water, minerals
• EXCRETION Get rid of waste materials
• REPRODUCTION Ability to produce like organisms
• IRRATIBILITY Respond to external stimuli
• GROWTH Cells grow larger . . . and dont forget
  . . .
• MR. NERIG also carries out the functions of
  life!

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1.1 Cell Theory

• 1.1.11
• Explain that cells in multicellular organisms
  differentiate to carry out specialized functions
  by expressing some of their genes but not others.
  (3)

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1.1 Cell Theory

• 1.1.12
• Define (1)
• Tissue A group of cells working together to
  perform a common function
• Organ A group of tissues working together to
  perform a common function
• Organ System A group of organs working together
  to perform a common function

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Prokaryotic cell

• 1.2.1
• Draw a generalized prokaryotic cell as seen in
  electron micrographs. (1)
• Use images of bacteria as seen in electron
  micrographs to show the structure.
• The diagram should show the cell wall, plasma
  membrane, mesosome, cytoplasm, ribosomes and
  nucleoid (region containing naked DNA).

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1.2 Prokaryotic Cells

• 1.2.2
• State one function for each of the following
  (1)
• cell wall forms a protective outer layer that
  prevents damage from outside and bursting if
  internal pressure is too high
• plasma membrane controls entry and exit of
  substances, pumping some of them in by active
  transport

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1.2 Prokaryotic Cells

• mesosome increases the area of membrane for ATP
  production. May move the DNA to the poles during
  cell division
• cytoplasm contains enzymes that catalyse the
  chemical reactions of meabolism and DNA in a
  region call the nucleoid

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1.2 Prokaryotic Cells

• ribosomes synthesize proteins by translating
  messenger RNA. Some proteins stay in the cell
  and others are secreted
• naked DNA stores the genetic information that
  controls the cell and is passed on to daughter
  cells

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1.2 Prokaryotic Cells

• 1.2.3
• State that prokaryotes show a wide range of
  metabolic activity including fermentation,
  photosynthesis and nitrogen fixation. (1)

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1.3 Eukaryotic Cells

• 1.3.1
• Draw a diagram to show the ultrastructure of a
  generalized animal cell as seen in electron
  micrographs. (1)
• The diagram should show ribosomes, rough
  endoplasmic reticulum (rER), lysosome, Golgi
  apparatus, mitochondrion and nucleus.

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electron micrograph
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1.3 Eukaryotic Cells

• 1.3.2
• State one function of each of these organelles
  (1)
• ribosomes protein synthesis
• rough endoplasmic reticulum (rER) synthesis of
  proteins to be secreted
• lysosome holds digestive enzymes
• Golgi apparatus for processing of proteins
• mitochondrion for aerobic respiration
• nucleus holds the chromosomes

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1.3 Eukaryotic Cells

• 1.3.4
• Describe three differences between plant and
  animal cells. (2)

Plant Cells
Structure
Animal Cells
Can produce its own food.
?
Chloroplast
X
Cannot produce its own food
Rigid, cannot easily change shape.
?
Cell Wall
X
Flexible, can easily change shape.
Stores large amounts of liquid (juice). Larger
size of cell.
?
Central Vacuole
X
Does not store large amounts of liquid. Smaller
size of cell.
Carbohydrates stored as starch.
Carbohydrates stored as glycogen.
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1.3 Eukaryotic Cells

• 1.3.5
• State the composition and function of the plant
  cell wall. (1)
• The composition of the plant cell wall should be
  considered only in terms of cellulose
  microfibrils.

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1.4 Membranes

• 1.4.1
• Draw a diagram to show the fluid mosaic model of
  a biological membrane. (1)
• The diagram should show the phospholipid bilayer,
  cholesterol, glycoproteins and integral and
  peripheral proteins.
• Use the term plasma membrane not cell surface
  membrane for the membrane surrounding the
  cytoplasm.
• Integral proteins are embedded in the
  phospholipid of the membrane whereas peripheral
  proteins are attached to its surface.

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1.4 Membranes

• 1.4.2
• Explain how the hydrophobic and hydrophilic
  properties of phospholipids help to maintain the
  structure of cell membranes. (3)
• Hydrophobic afraid of water
• Hydrophilic loves water

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1.4 Membranes
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1.4 Membranes
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1.4 Membranes
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1.4 Membranes
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1.4 Membranes

• 1.4.3
• List the functions of membrane proteins including
  (1)
• hormone binding sites
• enzymes
• electron carriers
• channels for passive transport
• pumps for active transport.

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1.4 Membranes

• 1.4.4
• Define diffusion (1)
• Diffusion is the passive movement of particles
  from a region of high concentration to a region
  of low concentration (down a concentration
  gradient), until there is an equal distribution.
• Define osmosis
• Osmosis is the passive movement of water
  molecules, across a partially permeable membrane,
  from a region of lower solute concentration (high
  water concentration) to a region of higher solute
  concentration (low water concentration).

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1.4 Membranes
Diffusion moves down the concentration gradient
just like a ball rolling down a hill. It cannot
roll uphill without energy.
High Concentration
Low Concentration
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1.4 Membranes

• 1.4.5
• Explain passive transport across membranes in
  terms of diffusion. (3)
• Requires no energy
• Moves from down the concentration gradient
• Some molecules pass through the membrane
• Some molecules use channels for facilitated
  diffusion

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1.4 Membranes
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1.4 Membranes

• 1.4.6
• Explain the role of protein pumps and ATP in
  active transport across membranes. (3)
• Requires energy, in the form of ATP, or adenosine
  triphosphate
• Molecules are pumped across the membrane UP the
  concentration gradient
• Pumps fit specific molecules
• The pump changes shape when ATP activates it,
  this moves the molecule across the membrane

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Active Transport
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1.4 Membranes

• 1.4.7
• Explain how vesicles are used to transport
  materials within a cell between the rough
  endoplasmic reticulum, Golgi apparatus and plasma
  membrane. (3)
• 1.4.8 Describe how the fluidity of the membrane
  allows it to change shape, break and reform
  during endocytosis and exocytosis. (2)

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1.4 Membranes

• Endocytosis the mass movement INTO the cell by
  the membrane pinching into a vacuole
• Exocytosis the mass movement OUT of the cell by
  the fusion of a vacuole and the membrane
• This is possible because the of the fluid
  properties of the membrane (able to break and
  reform easily, phospholipids not attached just
  attracted)

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Exocytosis
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Endocytosis
endo- and exo- -cytosis
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1.5 Cell Division

• 1.5.1
• State that the cell-division cycle involves
  interphase, mitosis, and cytokinesis. (1)

Mitosis
Cytokinesis
Interphase
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1.5 Cell Division

• 1.5.2
• State that interphase is an active period in the
  life of a cell when many biochemical reactions
  occur, as well as DNA transcription and DNA
  replication. (1)

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1.5 Cell Division

• 1.5.3
• Describe the events that occur in the four phases
  of mitosis (2)

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1.5 Cell Division

• PROPHASE - breakage of nuclear membranes and
  supercoiling of DNA to form visible chromosomes

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1.5 Cell Division

• METAPHASE - chromosomes line up along equatorial
  region of cell, attachment of spindle
  microtubules to centromeres

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1.5 Cell Division

• ANAPHASE - splitting of centromeres, movement of
  sister chromosomes to opposite poles as spindle
  microtubules shorten

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1.5 Cell Division

• TELOPHASE - uncoiling of chromosomes and
  reformation of nuclear membranes

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1.5 Cell Division
P rophase M etaphase A naphase T elophase P-MAT
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1.5 Cell Division

• 1.5.4 Explain how mitosis produces two
  genetically identical nuclei. (3)
• Synthesis of identical chromosomes in interphase
• Lining up during mitosis ensures that each new
  cell gets a copy of each chromosome

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1.5 Cell Division

• 1.5.5
• Outline the differences in mitosis and
  cytokinesis between animal and plant cells. (2)
• No centrioles in plant cells
• Cell plate formed in plants, membrane pinching
  in animal cells

Cytokinesis
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1.5 Cell Division
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1.5 Cell Division

• 1.5.6
• State that growth, tissue repair and asexual
  reproduction involve mitosis. (1)
• 1.5.7
• State that tumours (cancers) are the result of
  uncontrolled cell division and that these can
  occur in any organ. (1)