Dear students,
I know this week's lesson was quite heavy for most of you. Below are what we have learned & I hope i won't be writing this long in my next posting unless necessary.
1. Experiment: to observe the structures of plant cells & animal cells with a light microscope. (plant cells: onion &
Hydrilla sp. &
Elodea sp. epidermal cell; animal cells: Human cheek epidermal cells)
*under the light microscope, you are able to observe cell wall, plasma membrane, cytoplasm, nucleus, and sometime chloroplast.
a) similarities btw plant cell & animal cell : nucleus, cytoplasm, plasma membrane
b) In plant cell, there is cell wall, large/big central vacuole, chloroplasts (in photosynthetic cells)
c) In human/animal cells, there is no CW, No chloroplasts, usually vacuole not present.
2. Cellular components
A) which are not organelles:
i) Cell Wall (CW): (plant cell only)
*characteristics: rigid cellulose outer layer, permeable to all fluid.
*fn: protection, support, maintain shape of plant cell, prevent cells from bursting.
ii) Plasma membrane (PM):
*characteristics: composed of 2 lipid layers (phospholipids & proteins),thin flexible layer, semi-permeable.
* fn: controls/regulates the movements of substances entering & leaving the cell,separate the cell from its environment, allow exchange of substances.
iii) Cytoplasm:
*characteristic: jelly-liked substances, contains salts, dissolved gases, nutrients, enzymes, organic & inorganic substances. 70-90% are water. with organelles suspended in it.
*fn: medium for biochemical reactions & cellular metabolism.
An illustrated animal cell as seen under the electron microscope.
An illustrated plant cell as seen under the electron microscope.
B) Cellular components which are ORGANELLES:
*what are organelles?
->organelles are cellular components the can perform specific functions/specialised functions within the cell. Many are enclosed by membrane.
1) Nucleus:
* largest organelle.
* bounded by nuclear membrane - double membrane with pores.
* contains chromatin (DNA - Deoxyribonucleic Acid)
* chromatin? chromosome?
* has nucleolus - nucleolus makes RNA which is needed to make ribosomes. (ribosomes are produced by nucleolus)
#fn: direct & control all the activities of the cell.
2) Vacuole:
*small cavity contains cell sap & is enclosed by tonoplast (a SPM)
#fn: for storage, digestion & waste removal,
3) Ribosomes: (non-membrane bound particles)
* compact, spherical organelles, consists of RNA (Ribonucleic Acid) & proteins.
* either attached to rough ER or suspended freely in the cytoplasm.
#fn: sites of
protein synthesis.
4) Endoplasmic reticulum (ER):
* a system of flattened, membrane-bound sacs in the form of tubes & sheets.
* interconnected to nuclear membrane.
*form an extensive transport system in the cell.
* exists as Rough ER & Smooth ER
i) Rough ER:
* flat sealed sac which is continuous with the outer nuclear membrane, outer surface is covered with ribosomes that give it a rough appearance.
# fn: transport proteins made by ribosomes throughout the cell
ii) Smooth ER:
* tubular sealed sac - either extend from the rough ER or extend separately.
* does not have ribosomes
# fn: synthesis lipids & steroids hormone, breakdown of lipid-soluble toxins in liver cells,
5) Golgi apparatus/Golgi body/Golgi complex: (GA)
* a stack of flattened, membrane-bound sacs having form continuously at one end of the stack & budded off as vesicles at the other end.
#fn: as a processing, modification, packaging & transport centre of carbohydrate, proteins & glycoproteins. (site of Enzyme production & lysosome formation)
6) Mitochondrion: Mitochondria (plural)
* spherical to rod-shaped organelles with double membrane.
* inner membrane folded inwards to form projections called the cristae (crista - singular)
#fn: site for cellular respiration ('powerhouse' of the cell) to produce/generate/release energy (ATP- Adenosine Triphosphate).
7) Lysosomes:
* membrane-bound spherical vesicle formed by pinching-off from GA.
*contains digestive enzymes
#fn: as digestive compartment of the cell (intracellular digestion)
breaking down food, example in
Amoeba sp.
breaking down unwanted structure/molecules, example worn-out/old organelles, whole cell, old Red Blood Cell.
(common in animal cell, uncommon in plant cell because digestive enzymes are found in the vacuole)
8) Centrioles: (only found in animal cells)
* pairs of cylindrical organelles located outside/near the nucleus.
* made up of microtubules.
#fn: form spindle fibres during cell division, synthesise cilia & flagella in Unicellular organism.
9) Chloroplast: (only found in photosynthetic plant cells)
* lens-shaped organelle with double membrane.
*contains green pigment - chlorophyll
#fn: chlorophyll trap light energy & converts light E into chemical E during PS.
(diagram -- remember the stack of little round flat pillow? one stack is called granum, grana (plural))
3)Comparison btw the structure in animal cell & plant cell.
- refer to your table.
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Homework:
1) Do structure question 1 + 2 (Page 3)
2) State 2 similarities btw mitochondrion & chloroplast.
3) Compare a plant cell & human white blood cell.
4) What is chromosome?
5) You need to practise drawing & labelling a mitochondrion & chloroplast organelle in 2D image (not 3D). just like what i have drawn in the class.
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see you in the next lesson.
teacher sharon
13th Nov 2009
