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Science Notes
BIOLOGY
Cell Structures
-Cells are made of protoplasm.
-Protoplasm is also cytoplasm minus organelles.
-prokaryotic cells are cells with no real nuclei e.g. bacteria
-eukaryotic cells are cells with true nuclei
-Cell division = mitosis
-Light microscopes are able to observe living cells and resolution up to 2000x
-Electron microscopes are only able to observe fixed and dehydrated cells and resolution up to 2
million times
Microscope
-Eyepiece
-Body tube: connects the eyepiece to the objective lenses
-Objective lenses: 4x, 10x and 40x
-Revolving nosepiece: rotating part of the microscope holding the lenses
-Arm: where the microscope is to be held
-Coarse adjusting knob
-Fine adjusting knob
-Stage + stage clips
-Light source
-Diaphragm
-Base
*Magnification to 1d.p.*
-‘Chromatin’ is invisible, long and thread-like in the nuclei of cells, but ‘chromosome’ is visible as it is
condensed during mitosis, coiling around the protein.
-mitochondria are power plants for the cells, sites of respiration (uptake of oxygen) and they produce
potential energy.
-Cell membrane = plasma membrane
@ Cell membranes are partially permeable because if they are fully permeable, harmful substances
could diffuse in to the cells and useful substances could diffuse out.
-Vacuoles are surrounded by partially permeable membrane called tonoplast.
Science Notes
-Cell sap is content, not a structure. (fluid inside plant cells’ vacuoles) Contains water and dissolved
minerals such as glucose, mineral salts and amino acids)
-Cell walls are made of cellulose, thick and indigestible by the human body
--Another name for white blood cells: leucocytes.
-Guard cells allow gaseous exchange in leaves.
-Cytoplasm is made up of protoplasm and organelles.
Animal Cells
Irregular in shapes
Absence of Cell Wall
Numerous, small temporary vacuoles
Absence of Chloroplast
Plant Cells
Regular in shapes
Presence of Cell Wall
Usually large central vacuoles that contains
cell sap
Presence of Chloroplast
Red Blood Cell
-Contains haemoglobin, red pigment which absorbs oxygen
-No nucleus in order to increase the surface area to volume ratio, thus allowing faster diffusion.
-It has a biconcave shape, also to increase surface area to volume ratio to allow diffusion at a higher
rate.
-People suffering from sickle cell anemia will have their red blood cells the shape of a crescent, which
has a smaller total surface area to carry less oxygen than normal red blood cells. It will not block the
flow of blood, being stuck in the vessels I think…
Xylem Vessels
-Long hollow tubes formed from xylem tissues laid end-on-end with no cross walls and lumen empty
of protoplasm to allow smoother movement of water and dissolved mineral salts through the lumen.
-Thickly lignified cell wall to strengthen walls and prevent vessels from collapsing; lignin strengthens
the walls of xylem vessels.
- Carry ions and water to the rest of the plants; present in flowers and leaves as well.
*Division of labour refers to the breakdown of workload into smaller, more specific tasks to
increase efficiency.*
Diffusion, Osmosis and Active Transport
Science Notes
Diffusion
-Diffusion is the movement of molecules from a region of higher concentration to a region of lower
concentration down a concentration gradient.
-Steeper the concentration gradient (bigger the difference), faster the diffusion.
-E.g. Diffusion of carbon dioxide in and out of stoma of a leaf, diffusion of fatty acids and glycerol into
human ileum epithelial cell.
Osmosis
-Osmosis is the movement of water molecules from a region of higher water potential to a region of
lower water potential, through a partially permeable membrane.
-For plant cell, when it is placed in isotonic solution or any solution with higher surrounding water
potential, water will enter by osmosis and the vacuole increases in size. Then turger pressure from
cell walls is applied to keep the cell turgid, as water could not enter anymore due to this opposing
force.
-For plant cell, when in a hypertonic (surrounding water has a lower water potential) solution,) water
leaves cell by osmosis, vacuole decreases in size, cell membrane and cytoplasm shrinks away from
cell wall, (shrinkage known as plasmolysis and the cell is said to be plasmolysed.
-For animal cells, when they are placed in a hypotonic solution, (higher surrounding water potential)
water will enter through osmosis (net movement of water into the cells) and the cells will swell,
eventually burst as animal cells do not have cell walls to protect them. It is called lysis.
-For animal cells, when placed in hypertonic solution, the water leaves the cells by osmosis (net
movement of water out of the cells) and the cells shrink, little spikes appearing on the surface of
membrane. The shrinkage is known as crenation. *There must be lower water potential
surrounding the cells for this to take place*
-For animal cells placed in isotonic solution, there is no net movement of water in or out of cells.
Active Transport
-A process in which energy is used to move particles of a substance from a region of lower
concentration to a region of higher concentration, against a concentration gradient.
-E.g. epithelial cells in ileum absorbing glucose and amino acids through active transport.
- Active transport stops when there is no carbon dioxide is supplied to a cell.
- Active transport stops when the required amount of substance in the cell is reached.
Diffusion
Osmosis
Active Transport
Science Notes
Along a concentration gradient
Along a water potential gradient
Against a concentration gradient
Does not require energy (passive
process)
Does not require a partiallypermeable membrane
Involves all particles
Does not have to take place in
living cells
Does not require energy
(passive process)
Requires a partially-permeable
membrane
Involves only water molecules
Does not have to take place in
living cells
Requires energy (active
process)
Requires a partially-permeable
membrane
Involves only selected particles
Have to take place in living cells
(energy requiring)
Micro-organisms
Viruses
-Unicellular organisms
-Viewed only under an electron microscope
-Each contains a strand of DNA or RNA
-They are non-living cells, as they do not have nuclei, cell membranes or cytoplasm (no organelles)
-Have protein coats/capsids that help to attach them to a host cell; surrounded by a coat of protein
units.
-Classified by the type of nucleic acid (DNA or RNA) and the shapes of their protein coats.
Bacteria
-Unicellular organisms
-Can be seen under light microscope
-All have circular DNA in nucleoid region. There is presence of cytoplasm, cell membrane and
numeral food store (glycogen store, vacuole).
-Some have:



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Plasmid DNA, which is usually used for genetic engineering, but no nuclear membrane, thus
prokaryotic.
Some bacteria have pili which protect the cell surface and help to attach the bacteria to other
surfaces
Polysaccharide capsule, big carbohydrate molecule that provides additional protection for the
cells.
Flagellum which helps in movement
-They do not have vacuoles.
-Reproduce by binary fission.
-All have peptidoglycan cell walls, which can be weakened by antibiotics for the cells to swell and
burst.
-Three shapes: rods (bacilli), spheres (cocci) and spiral (spirilla)
Science Notes
Fungi (unicellular)
-Unicellular organisms e.g. Yeast
-Can be seen under light microscopes
-DNA with histones (proteins), glycogen stored in vacuole, chitin cell walls.
-Presence of organelles such as cell membrane and cytoplasm, nuclear membrane as well;
eukaryotic cells.
-Ecologically, fungi are important because they are natural decomposers and heterotrophic, returning
nutrients and mineral salts back to the environment, fertilising the soil and preventing trash from
building up.
-Economically, they provide us with food and medicine; fungicide treats athlete’s foot.
*Heterotrophic refers to deriving energy from other organisms*
*Autotrophic refers to making one’s own energy*
Fungi (multicellular)
-Multicellular organisms
-Can be seen with naked eyes
-DNA with histones (proteins), glycogen stored in vacuole, chitin cell walls.
-Many cells joined together
Penicillium-consists of hypha, joined into hyphae, forms mycelium; make cheese and a decomposer.
Mycelium is the asexual reproductive part of fungi, and it is through a mycelium that a fungus
absorbs nutrient.
Amoeba and Paramecium reproduce asexually.
Science Notes
Fermentation
Fermentation-Cheese
Lactose (sugar in milk) + lactobacillus (bacteria) with no oxygen  lactic acid + energy
(bacteria need energy to grow)
Lactic acids cause the milk to be sour and curdle. Now enzyme rennet is added to the
fermented milk and the acidic medium in the lactic acid allows reaction of the milk to this
enzyme.
Soluble milk protein (caseinogen) + enzyme  insoluble milk protein (casein)
This happens in the stomach as well, and the digestive juice, or rather, enzyme called pepsin,
causes the milk protein to solidify for it to stay and be digested and absorbed. The liquid part
of the curdling milk protein is called whey. The fermented milk is to be mixed with other fungi and
bacteria to make cheese.
Fermentation-Bread
Flour contains starch, enzyme amylase and protein. Warm water is mixed with flour, amylase feeds
on starch and dough forms. Yeast is then mixed with dough. Due to lack of oxygen in the dough,
yeast is able to respire anaerobically, fermenting the sugar to carbon dioxide and alcohol.
Carbon dioxide allows the bread to rise (alcoholic fermentation), giving it a porous texture,
also creating the holes in bread. Alcohol will evaporate and yeast will be killed when baking.
Fermentation-Beer Brewing
Malting involves providing barley seeds with suitable conditions to make them germinate. When
this happens, enzymes in the seeds convert starch in the seeds into sugar (glucose). This is
required before fermentation because fungi and bacteria can only feed on sugar.
Sugar + yeast in the absence of oxygen  alcohol + carbon dioxide + energy
Micro-organisms as green agents
Some bacteria secrete enzymes to digest solid waste into soluble, harmless substances and the gas
carbon dioxide. The liquid that results is filtered and disease-causing organisms removed before
being discharged into the sea. The digested solid sludge is either dried to be used as fertiliser, or
broken down by bacteria to be used as landfill material.
Science Notes
Digestive System
Carbohydrates: -immediate source of energy
-excess glucose stored in liver as glycogen
-usually as starch in a normal diet
-cellulose
Fats: -Provides twice the amount of energy as carbohydrates but harder to oxidise.
-Stored under skin to insulate body against heat lost.
- All natural fats go under digestion, absorption and assimilation. Thus man-made fats will
prevent obesity as they are not digested, nor absorbed.
- All fats, natural or not, go under emulsification.
- If fats are not emulsified, they will have a less surface area to volume ratio.
Protein: -Building of new cells, growth and repair of cells
-Used to form enzymes and hormones.
-Haemoglobin
Dietary Fibre: -To be digested by cellulase which is not present in the human body
-Helps in peristalsis in by increasing the speed of movement of faeces to prevent overabsorption of water (prevents constipation)
Water: -Transport nutrients and waste around the body, control body temperature and is needed for
certain reaction such as hydrolysis in digestion.
Vitamins: -Vitamin A helps with eyesight and healthy skeleton and soft tissues.
-Vitamin C involves growth and repair of tissues. Lack of this vitamin: scurvy (bleeding gum,
spots on skin, loss of teeth)
-Vitamin D helps in the absorption of calcium (go under the sun). Lack of this: rickets (thin,
brittle or misshaped bones)
Science Notes
Minerals: -Iron is an integral part of enzymes and proteins, especially those involved in transportation
of oxygen and cell growth, like haemoglobin. Lack of this: nutritional anaemia (pale, tired).
-Calcium is essential to carry out many metabolic processes, like muscle function and
hormone secretion. It is stored in bones and teeth to support the body structure and
function, related to Vitamin C.
Mouth:
Starch + Amylase  Maltose
Stomach:
Protein + Pepsin  Polypeptides
-Churns and liquefies food by peristalsis. It thus helps in the digestion of food.
-Acidic, so contains pepsin ONLY to turn protein into polypeptides.
-It is not corroded by hydrochloric acid because the walls of stomach produce mucus which protects
the stomach.
Duodenum:
Proteins + Trypsin  Polypeptides + Erepsin  Amino Acids
Starch + Amylase  Maltose + maltase  Glucose
Lactose + Lactase  Glucose + Galactose (simple sugar)
Sucrose + Sucrase  Glucose + Fructose
Fats (lipids) + lipase  Glycerol + Fatty acids
-Fats are first emulsified by bile salts, broken into fatty droplets. This increases the surface area to
volume ratio and thus increases the rate of digestion by lipases. This is a physical break-up.
-Lipases came from bile of gale bladder
Ileum:
-The presence of villi and microvilli increases surface area to volume ratio, thus increasing the rate of
absorption, mostly by active transport of glucose and amino acids, as well as osmosis for water, and a
small percentage of diffusion of fatty acids and glycerol.
Colon:
Science Notes
-Absorbs water and mineral salts from undigested food.
Rectum:
-Stores faeces temporarily.
Gall Bladder:
-Releases bile into duodenum; stores bile
Pancreas:
-Produce pancreatic juices that contain enzymes to digest carbohydrates, protein and fats.
-Secretes insulin and glycagon (hormone) to help control blood glucose concentration hence control
carbohydrate metabolism.
Liver:
-Produces bile.
- Liver store the glucose that is converted into glycogen.
- When there is a short in the supply of glucose, amino acids are converted into glucose.
Science Notes
Notes Gathered
-Magnification = Length of drawing divided by Length of actual object
-Chloroplast is the site of photosynthesis and manufacture of glucose
-Red blood cells have cell membrane and cytoplasm that can be labelled as well
-Red blood cells carry oxygen from lungs to all parts of the body.
-The biconcave shape of the red blood cell is to increase surface area to volume ratio to increase the
rate of oxygen diffusion.
-An organ is made up of different tissues.
-An organ system is a system of different organs working together to accomplish a specific task.
-Food placed in brine (concentrated salt solution) and syrup do not turn bad because the water
potential outside the cells of the microorganisms is lower than the water potential inside the cells, so
water leaves the cells by osmosis, thus leaving the cells crenated and the microorganisms dead.
-If it is obvious that the question is about active transport, a labelled, funny looking structure is most
likely the mitochondrion which is the site of respiration of the cell, generating energy for active
transport to take place.
-Layer of oil/wax is to reduce water loss.
-Lactobacillus is added to lactose to turn it into lactic acid. The acidic medium in the lactic acid allows
the enzyme rennet to convert caseinogen into casein.
-We are to keep our work area clean so that no foreign bacteria are introduced to affect the bacteria
being studied.
-If the question purposely state that there is oxygen available with root hair cells, it means that there is
respiration. So the root hair cells will take in the oxygen, water and minerals to respire. (皿)
-Aseptic techniques are important because it ensures that only one type of micro-organism is present
in the growth media and that the micro-organism does not contaminate or cause diseases.
-All enzymes speed up the rate of reaction only.
-Bananas provide more carbohydrate. (Bananas are full of starch)
-Fish contains the most amount of protein.
- A newly cut onion shoot bends outwards because the inner cells are released from the restriction of
the thick-waxed epidermal cells.
- During the culturing process of bacteria such as Escherichia coli (E.coli),
1. Label at the base so that even if the base is moved the labelling are still at the correct quadrants,
thus avoiding confusion.
Science Notes
2. Petri dish should be inverted so that condensed water droplets on the cover do not fall onto the
bacteria and affects their growth.
- Sperm have many mitochondria to generate more energy to move. They also have their cell
membranes extended into flagellums to help in their movements.