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F 6 Biology - Ch 4: Cellular Organization
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The cell is the fundamental unit of life. The modern theory of cellular organization states that:
1. All living organisms are composed of cells
2.
3.
4.
Microscopy
Structure of the light microscope: uses light to view specimens
Simple microscope - uses _____ magnifying lens
Compound microscope - use _____ magnifying lenses
Resolution (resolving power) : the degree of detail which can be seen with a microscope
Staining and preparation of slides for the light microscope
- in order to make transparent material visible or to enhance the ________ of a specimen
Structure of the electron microscope
- uses electron beam to pass through specimen and directed onto a screen which
develops black & white photographs (photoelectron micrographs)
- two types:
transmission electron microscope - for very thin object to produce flat images
scanning electron microscope - for producing three-dimensional images
Preparation and staining of material for an electron microscope
- a long and complicated process
Comparison between light and electron microscopes
Light Microscope
Advantages
1. Cheap
2. Small & portable
Electron Microscope
Disadvantages
1.
2.
3. Unaffected by magnetic field
3.
4. Easy to prepare materials
4.
5. Materials rarely distorted by preparation
5.
6.
6. Natural colour of specimen can be seen
Disadvantages
1.Magnifies up to 2000 x
2 Depth of field is restricted
3 Lower resolution
Advantages
1.
2.
3.
F 6 Biology - Ch 4: Cellular Organization
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4.1 Cytology - the study of
4.1.1 The structure of prokaryotic cells
primitive cells: in bacteria & blue-green bacteria
4.1.2 Structure of the eukaryotic cell
- true cells: develops from prokaryotic cells
- Advantages of membrane-bounded organelles in eukaryotic cells:
1. Organelle membranes increases the surface area to volume ratio for enzymatic reactions
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F 6 Biology - Ch 4: Cellular Organization
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Table 4.1 Comparison of prokaryotic and eukaryotic cells
Prokaryotic Cells
1 No distinct nucleus
2 No chromosomes but circular strands of DNA
3 No membrane-bounded organelles such as
mitochondria
4 Smaller ribosomes
5 Flagella (if present) lack the 9+2 fibril
structure
6 No mitosis or meiosis occurs
Eukaryotic Cells
F 6 Biology - Ch 4: Cellular Organization
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4.2 Differences between plant and animal cells
Plant Cells
Animal Cells
4.2 Cell Ultrastructure
Separation of cell organelles - cell fractionation
1. Tissue cut into pieces
1. Ground in a homogenizer
2. Differential centrifugation - cell wall fragments, nuclei, chloroplasts,
mitochondria, endoplasmic reticulum fragments,
and finally ribosomes
4.2.1 Cytoplasmic matrix - hyaloplasm or cytosol
- a colloidal suspension of many chemicals:
ions, e.g.
organic molecules, e.g.
storage material, e.g.
- many biochemical processes occur in cytoplasm
- carries out cytoplasmic streaming
4.2.2 Cell membranes
Functions:
Structure
The protein-phospholipid sandwich (Davson-Danielli model)
- phospholipid molecules form a bimolecular layer:
hydrophobic tails hydrophilic heads - protein layer:
F 6 Biology - Ch 4: Cellular Organization
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The fluid-mosaic model (Singer-Nicholson model)
- phospholipid molecules unchanged but is capable of movement (fluid)
- protein molecules varied in size and have less regular arrangement (mosaic):
some proteins occur on the surface of the phospholipid layer (peripheral);
some extend into the phospholipid layer (integral);
some extend completely across the phospholipid layer (transmembrane)
- proteins appear dotted throughout the phospholipid layer in a mosaic pattern
- proteins have many functions, e.g. support, transport and
their specificity enables them to perform many specific functions which vary from cell to cell
Membranous Organelles
4.2.3 The nucleus
nuclear envelope:
nucleoplasm: cytoplasm of the nucleus
chromatin:
heterochromatin: denser, more darkly staining areas of chromatin
nucleolus:
Functions of a nucleus:
1.
2. To act as a control centre for activities of a cell
3.
4.
5 Essential for cell division
F 6 Biology - Ch 4: Cellular Organization
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4.2.4 The chloroplast
plastids: double membraned organelles containing chlorophyll & carotenoids and carry out
photosynthesis
chloroplast envelope:
stroma:
grana:
thylakoid: flattened sacs of granum holding chlorophyll for photosynthesis, intergranal lamellae
(large thylakoid) join grana together
starch grains: temporary stores for the products of photosynthesis
DNA & oil droplets
F 6 Biology - Ch 4: Cellular Organization
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4.2.5 The mitochondrion
Double membrane:
outer controls the entry & exit of chemicals;
inner is folded to form cristae to increase the surface area for respiration to occur.
The surface of the cristae have stalked granules along its length.
Matrix:
Functions as sites for stages of respiration;
Highly active cells may possess up to 1000 mitochondria in a single cell, e.g. sperms & muscles.
4.2.6 Endoplasmic reticulum
- an elaborate system of membranes forming a cytoplasmic skeleton
- an extension of the out nuclear membrane
cisternae: flattened sacs formed by the membranes
rough endoplasmic reticulum:
smooth endoplasmic reticulum: membranes lack ribosomes
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Functions of the ER:
1 Provides a large surface area for chemical reactions.
3 Produces proteins, especially enzymes
5 Collects and storing synthesized materials
4.2.7 Golgi apparatus (dictyosome)
- similar to smooth ER but is more compact
vesicles:
- normally only one Golgi apparatus in animal cells but a large number of
stacks known as dictyosomes in plant cells
- well developed in secretory cells and neurones for secretory functions
Functions:
1 adding carbohydrates to proteins to form glycoprotiens
3 produce new cell walls by secreting carbohydrates
5 form lysosomes
4.2.8 Lysosomes
- bounded by a single membrane which
contains enzymes (mostly hydrolases)
- abundant in secretary cells & in
phagocytic white blood cells
Functions:
1 Digest material which the cell consumes from the
outside by phogocytosis, e.g. white blood cells
digest bacteria, amoeba digests food.
3 Release enzymes outside the cell (exocytosis) to
break down other cells, e.g. reabsorption of tail of
tadpoles during metamorphosis
Therefore, they are
F 6 Biology - Ch 4: Cellular Organization
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4.2.9 Microbodies
- small spherical membrane-bounded
bodies; slightly granular structure
- contains enzymes (mostly catalase) to
break down H2O2:
nucleus
A
B
C
D
E
- H2O2 is a potentially toxic by-product of many biochemical reactions in cell,
particularly active cells like the liver cells
4.2.10 Vacuoles
- tonoplast:
- containing a solution of mineral salts, sugars, amino acids, wastes and
sometimes anthocyanins
- large and central in plants
numerous but small in animal cells, e.g. food vacuole, phagocytic vacuole
and contractile vacuole
Functions:
1 temporary food reservoir of sugars & amino acids
3 temporary stores for wastes, e.g. tannins, and to be removed through leaf cells when leaves fall
5 provide turgidity to herbaceous plants & seedlings
Non-membranous Structures
4.2.11 Ribosomes
- small cytoplasmic granules of RNA molecules for __________________________
- around 20 um in diameter in eukaryotic cells (80S)
but slightly smaller in prokaryotic cells (70S)
- account for 20% of the mass of a cell
polysomes:
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4.2.12 Storage granules
- soluble form as sugars in vacuoles of plant cells
- insoluble forms:
starch grains - in chloroplasts & cytoplasm;
in specialized leucoplast (amyloplast)
glycogen granules lipid droplets –
Leucoplast are colourless plastids (double membraned organelles in plants)
4.2.13 Microtubules
- slender unbranched tubes about 20 nm in diameter & several um in length
Functions:
1 act as an internal skeleton (cytoskeleton) for the cells &
determine their shapes
3 form a framework along which the cell wall is laid down
5 form centrioles of the spindle during cell division
4.2.14 Cilia and flagella
- cilia are shorter & more numerous than flagella
- both about 20 um in diameter;
cilia about 10 um long, flagella about 100 um
Functions:
1 To move an entire organism, e.g. cilia of parameucium and flagellum of bacteria
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4.2.15 Centrioles
- same basic structure as basal bodies of cilia
centrosome:
* Higher plants do not have centrioles, but they form spindle for cell division
4.2.16 Microfilaments
- very thin strands about 6 nm in diameter
- with actin & myosin proteins (similar to
muscles), thus probably play a role in movement within cells/cell as a whole
4.2.17 Microvilli
- finger-like projection about 0.6 um in length on the membranes of cells
brush border:
- actin filaments within the microvilli allow them to
contract, with a larger surface area created,
microvilli facilitate _______________,
e.g. _________________________
4.2.18 Cellulose and cell wall
β-glucose → cellulose chain → micelle → microfibril → fibril embedded
in polysaccharide matrix
Functions:
1 To provide support for young seedlings & herbaceous plants
3 Freely permeable to water, thus allow movement of water in the plant, e.g. in the cortex of roots
4. Lignin:
Cutin:
Suberin
F 6 Biology - Ch 4: Cellular Organization
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4.3 Movement in and out of cells
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1._____________ 2._____________ 3._____________ 4._____________ 5._____________
4.3.1 Diffusion - the process _______________________________________________
_
Rate of diffusion depends upon:
1. The concentration gradient
2. The distance over which diffusion takes place
3. The area over which diffusion takes place
4. The nature of any structure across which diffusion occurs
5. The size & nature of the diffusing molecule
4.3.2 Facilitated diffusion: is a special form
of diffusion which allows more rapid
exchange.
It involves
4.3.3 Osmosis - the passage
osmotic pressure: (old term – a +ve value): pressure applied to the system to prevent osmosis to
occur
water potential:
- water potential of pure water is ______
- water will diffuse from a region of ______ water potential to a region of ______ water potential
hypotonic solution:
hypertonic solution:
isotonic solution:
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4.3.4 Active transport
- energy is spent to drive the transport of molecules across membranes because
________________________________________________________________________
- Mechanism: through proteins that span the membrane
Characteristics of cells & tissues carrying active transport:
1 presence of numerous mitochondria
3 high respiratory rate
- any factors that affect respiratory rate will affect active transport,
e.g.
4.3.5
Phagocytosis - the process
cell invagination to contain particle
→ vacuole
→ lysosomes fuse with vacuole
→ enzymes digest particle
→ useful materials absorbed
- examples:
F 6 Biology - Ch 4: Cellular Organization
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4.3.6 Pinocytosis - cell __________
- similar to phagocytosis but vacuoles (pinocytic or micropinocytic vesicles) are smaller
- for intake of liquids
endocytosis: both pinocytosis and phagocytosis are methods by which materials are taken into the
cell in bulk
exocytosis:
Functions of lysosomes:
1 Digestion of material taken in by endocytosis
2 Autophagy: a process to remove unwanted structures within the cell
3 Release of enzymes outside the cell (Exocytosis), e.g. osteoclasts (remodelling of bones)
4 Autolysis: self-destruction of the cell
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