F 6 Biology - Ch 4: Cellular Organization Name: ( )

F 6 Biology - Ch 4: Cellular Organization Name: ( )

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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 Electron Microscope

Advantages 1. Cheap 2. Small & portable 3. Unaffected by magnetic field 4. Easy to prepare materials 5. Materials rarely distorted by preparation

6. Natural colour of specimen can be seen

Disadvantages

1.

2.

3.

4.

5.

6.

Disadvantages 1.Magnifies up to 2000 x 2 Depth of field is restricted

3 Lower resolution

Advantages

1.

2.

3.


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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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Table 4.1 Comparison of prokaryotic and eukaryotic cells

Prokaryotic Cells Eukaryotic 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


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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:


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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


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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


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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


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A

B

C

D

E

nucleus

4.2.9 Microbodies

- small spherical membrane-bounded

bodies; slightly granular structure

- contains enzymes (mostly catalase) to break down H2O2:

- 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


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4.3 Movement in and out of cells 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:


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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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97-II-1(c)


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83-II-1

F 6 Biology - Ch 4: Cellular Organization Name: ( )

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