environmental science

1. P a g e 1 | 22
BROAD TOPICS BIOLOGY CXC EXAM 2022
REVISION GUIDE
1. YOU ARE NOT EXPECTED TO GO THROUGH THIS ENTRIRE DOCUMENT IN A DAY
2. TAKE YOUR TIME, THE DIFFERENT TOPICS ARE COLOUR CODED, YOU CAN DO ONE
TOPIC A DAY
3. SET UP A STUDY PLAN AND STICK TO IT!
4. USE YOUR PAST PAPER QUESTIONS (PPQ) TO PRACTICE! PRACTICE! PRACTICE!
5. REMEMBER TO EXPLAIN AND ELABORATE ON YOUR RESPONSES, YOU MAY DO THIS
BY GIVING A DEFINITION, EXAMPLES, DRAW WHEN YOU CAN, STATE THE
IMPORTANCE, ETC.
NOTE THAT THESE ARE THE BROAD TOPICS FOR PAPER TWO
YOU WILL STILL NEED TO REVISE EVERYTHING FOR PAPER 1
IN YOUR CLASSROOM YOU HAVE ACCESS TO PAPER 1s AND
AN ANSWER SHEET

2. P a g e 2 | 22
1. Growth In Plants Versus Growth In Animals
Definition:
Growth is the permanent increase in size caused by an increase in the number and size of cells.
Plants differ from animals in their manner of growth. As young animals mature, all parts
of their bodies grow until they reach a genetically determined size for each species. Plant
growth, on the other hand, continues throughout the life span of the plant and is
restricted to certain meristematic tissue regions only (well defined growing points).

3. P a g e 3 | 22
Details in mechanisms of plant growth:
https://www.youtube.com/watch?v=RqCqUEu9nY4&list=TLPQMTQwNTIwMjJlO1bA99Ifhg&index=2
Focus on meristematic cells, auxin, gravitropism/geotropism, phototropism, the other parts of the video
does not apply at this level

4. P a g e 4 | 22
2. Germination
Definition:
The growth and development of a seed to a new plant.
OR
The process where the seedling bursts out of the seed coat once given the correct conditions.
Visual learners: https://www.youtube.com/watch?v=RmYk6r25n4s
Importance:
Seed germination determines continuous plant production necessary for human survival with
regards to the supply of medicinal plants, feed for animal grazing, carbon sinks, habitats for other
organisms and food security among other things.
Conditions:
- WATER/MOISTURE (TAKEN THROUGH MICROPYLE): NEEDED FOR CHEMICAL REACTIONS/ TO START THE SEED’S
ENZYMATIC ACTIVITY AND METABOLISM. THE WATER INTAKE INSIDE THE SEED CAUSES THE SEED COAT TO
RUPTURE, THUS ALLOWING THE SEEDLING TO EMERGE FROM THE SEED.
- OXYGEN: NEEDED FOR RESPIRATION
- WARMTH: NEEDED FOR ENZYME EFFICIENCY
- LIGHT: A STIMULUS FOR GROWTH SO THAT SEEDLING MAY BE GUIDED ABOVE GROUND

5. P a g e 5 | 22
Process:
a) The seed rapidly absorbs water from the environment causing the seed coat to swell and
become soft.
b) The absorbed water activates the enzymes present inside the seed that starts the growth phase
in the embryo. The seed begins respiration by absorbing oxygen and utilizing the stored food to
form proteins necessary for its growth
c) As the rate of respiration increases, the seed coat ruptures to form a radical which later
develops into a primary root, while the plumule develops into a shoot. During this period, the
enzymatic activity remains at an all-time high.
d) The final step of seed germination when the first embryonic leaf or the cotyledon appears.
Gradually, tiny leaves sprout from the shoot ends, these are known as foliage leaves. During this
initial phase of development, the baby plant continues to use the food stored within the seed.
Once this phase is complete, it starts synthesizing its own food by photosynthesis

6. P a g e 6 | 22
3. Nutrition: Heterotrophic, Autotrophic
Definition:
the way all living things obtain or make food to provide nourishment essential for growth and
maintenance of life
Differentiation:
Autotrophic: self-feeding, organisms who carry out autotrophic nutrition using simple molecules
from their environment to create their own food. Photosynthesis is an example of autotrophic
nutrition; plants use sunlight, carbon dioxide and water to create glucose and oxygen. All
organisms who are autotrophs are PRODUCERS, they supply/ start all the food chains as they do
not have to rely on other organisms for food.
Heterotrophic: other feeding, unlike autotrophs, heterotrophs do not make their own food,
they are CONSUMERS, as they depend on other organisms to feed. There are three main types
of consumers: herbivores, omnivores, and carnivores.
Heterotrophs obtain ready-made food from the environment.
Visual learners: https://www.youtube.com/watch?v=h3ychzika4U
Nutrient:
a chemical substance found in foods that provides nourishment essential for growth and
maintenance of life
Just in case:
- know the sources of the major nutrients (carbohydrates, proteins, fats, fibre, minerals, vitamins,
water) and related deficiency diseases (minerals and vitamins included)
- Know the food test for starch, reducing and non-reducing sugars, protein, fats/oils
o Starch test – reagent: iodine – positive: blue-black – negative: brown
o Reducing sugar – regent: benedicts solution (blue) – positive: orange to brick red –
negative: remains blue
o Non reducing sugar – regent: benedicts solution, boiling and hydrochloric acid to break
bonds – positive: orange to brick red – negative: remains blue
o Protein – regent: biurets solution (blue) – positive: violet/purple – negative: remains
blue
o Fats/ oils: reagent: emulsion test (ethanol then water) – positive: white cloudy emulsion
– negative: no emulsion
- Enzymes, know their structure: they are proteins and therefore have a folded structure with an
active site. They are catalysts, specific (lock and key, complementary to their substrate) work
best at pH and temperature. Optimum temperature in humans 37 degrees Celsius anything
above that the enzyme is denatured (looses chape and so substrate can no longer fit in active
site) Low temperatures decreases the energy of the reactants and so they cannot collide to carry
out the chemical reaction. Activity of the enzyme slow down as it moves away from optimum
conditions. Different enzymes have different optimum pH, pepsin 2, salivary amylase 7,
pancreatic amylase 9.
- Teeth: know how to label and the functions of each type of tooth

7. P a g e 7 | 22
4. Photosynthesis
Definition:
The process where plants make their own food using sunlight, carbon dioxide and water to
produce glucose and oxygen.
Word and chemical equation:
DO NOT FORGET THE SUNLIGHT ABOVE THE ARROW AND THE CHLOROPHYLL
UNDER THE ARROW
Raw materials:
Fate of products:
Glucose -> used for respiration, excess stored as starch, converted to sucrose for transport in
the phloem, modified to create other nutrients like amino acids.
Oxygen -> some used in respiration, the excess is excreted as a waste product via diffusion
through the stomata
Stages:
Light stage: can only occur during the day, sunlight used to split the water =molecule into
hydrogen and oxygen
Dark stage: can occur during the day and the night. The hydrogen form the light stage combines
with the carbon dioxide to create glucose

8. P a g e 8 | 22
Internal and external Structure of the leaf:
Adaptations: green due to chlorophyll to
absorb sunlight. Broad and flat, to increase
the surface area for maximum absorption.
Thin so diffusion and sunlight penetration can
occur rapidly. Stomata to allow gases to
diffuse in and out of the leaf. Veins:
containing xylem to transport water and
phloem to transport food. Petiole/ leaf stalk
to change position of the leaf so it can get
maximum sunlight.
Adaptations: Waxy cuticles prevent
water loss and transparent to allow
sunlight to penetrate. Upper epidermis
transparent to allow light to enter.
Palisade layer, closely packed together
right under the upper epidermis,
contains many chloroplasts to absorb
sunlight and carry out photosynthesis.
Mesophyll spongy layer contains some
chloroplast to also carry out
photosynthesis. Air spaces allow
movement of gases around the leaf.
Stoma, holes in the leaf that allows the
gases to diffuse in and out the leaf.
Photosynthesis test:
Starch Test: the leaf is boiled in water to damage the cell membrane and release
chlorophyll. After boiling, the leaf is submerged in a test tube of alcohol placed in a hot water
bath to dissolve chlorophyll and turn the leaf white (this is important as the colour change
would be seen more clearly on a white leaf). Precaution is to prevent direct contact between the
flame and the alcohol since it is flammable so there is a need to avoid starting a fire. After
submerging in the alcohol, it becomes brittle and so it is dipped back into water so that it may
be soft again to prevent it from tearing. The leaf is spread on a white tile and covered in iodine.
The green parts of the leaf that has chlorophyll and so has the ability to photosynthesize, will
turn black to indicate starch is present. The other parts of the leaf without chlorophyl will take
the colour of the iodine, i.e., brown.
The presence of starch proves that photosynthesis is occurring because photosynthesis produces
glucose. However, excess glucose is stored as starch and thus if starch is present then that would
indicate that glucose was present, Glucose cannot be produced without photosynthesis.
Testing a variegated leaf shows that chlorophyll is a requirement for photosynthesis because only the
green parts of the leaf where chlorophyll was present will turn blue-black on the white leaf. Chlorophyll
is the green pigment that absorb sunlight which is needed to split the water molecules to supply
hydrogens for the dark stage. Without chlorophyll, the light stage would not be able to occur and so
glucose production would be prevented as well.
Oxygen Test: a beaker is filled with water and a water plant is placed in the beaker
under a funnel. An inverted test tube is placed over the funnel. With exposure to light the plant
will start to produce gas due to it photosynthesizing. To ensure the gas is oxygen the inverted
test tube is taken from the set up and a glowing splint is inserted into it. If the glowing splint
rekindles that is a positive test to show that the gas captured is oxygen.

9. P a g e 9 | 22
Limiting Factors of photosynthesis:
temperature, carbon dioxide, light intensity, and water
Be sure to explain the shapes of the graphs.

10. P a g e 10 | 22
5. Plant cells versus animal cells
a. Structure and function of cell
b. Organelle/ components

11. P a g e 11 | 22
Organelle Location Function
Cell wall Plants only Protects and support the cell, it composed of a network
of cellulose that makes it rigid
Cell membrane Both plants and animals Semi permeable – controls what comes in and out of
cell
Cytoplasm Both plants and animals Jelly like substance that houses the other organelles;
site of some chemical reactions
Nucleus Both plants and animals The brain of the cell, controls all the activities within the
cell and houses the organism’s genetic material
vacuole Large permanent vacuoles in
plants
Small temporary vacuoles in
animals
In plants the vacuole stores water and waste materials
In animals the vacuoles transport substances around
the cell
Mitochondria Both plants and animals The powerhouse of the cell, site of respiration as it
creates energy
Chloroplast Plants only Contains chlorophyll that captures sunlight used for the
process of photosynthesis
Ribosomes Both plants and animals Produces proteins
Starch grains Plants only Excess glucose is stored in starch grains
Glycogen Animals only Excess glucose is used as glycogen in animals
Golgi bodies/apparatus Both plants and animals Receives proteins from other materials from the
endoplasmic reticulum. Sort, modifies and packages
these materials to be exported from the cell.
Endoplasmic reticulum Both plants and animals Carries protein and other materials from one part of the
cell to the next
Differences:
1) plant cells have a fixed shaped while animal cells have irregular shapes.
2) Plant cells have chloroplast, animal cells do not.
3) Plants store excess sugar as starch while animals store it as glycogen.
4) Plants have large permanent vacuoles while animals have temporary small ones.

12. P a g e 12 | 22
c. Osmosis
Definition:
The movement of water molecules from a place of high concentration to a place of low
concentration across a semipermeable membrane. It is an example of passive transport as no
energy is required since the movement is down a concentration gradient.
Importance:
- All living things have certain requirements they must satisfy to remain alive maintain
homeostasis.
- These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and
eliminating wastes.
- These tasks ultimately occur at the cellular level and require that molecules move through the
membrane that surrounds the cell.
- Molecules move through the cell membrane by diffusion, osmosis, or some other process
Types of solutions
Isotonic – this solution has the same concentration of water as in the cell
Hypotonic – this solution is diluted i.e., contains more water molecules than in the cell
Hypertonic – this is a concentrated solution contains less water molecules than the cell i.e., the
solution has more solute particles than solvent particles
Just in case
Know how animal vs plant cells behave in the different solutions

13. P a g e 13 | 22
Cell specialization
Animal
Specialized Cell
Structure KNOW HOW TO IDENTIFY, DRAW AND
LABEL
Function & Adaptation
Ovum/ egg To carry the 23 chromosomes for the mother.
- Have a large cytoplasm that feeds the
developing embryo
- The outer layer of the egg only allows
one sperm to enter
sperm To carry the 23 chromosomes of the father
and to fertilize the egg.
- Acrosome contains chemicals to
penetrate the outer layer of the egg
- The midpiece of the sperm contains a
lot of mitochondria to create energy
for the sperm to travel
- Has a tail in order to swim and deliver
the chromosomes to the egg
Red blood cell To transport oxygen
- Red due to haemoglobin the binds
oxygen
- Biconcave shape which increases the
surface area to allow efficient diffusion
and to transport more oxygen
- Mature red blood cells have no
nucleus to allow for more space for
oxygen to be transported
- Small and flexible to easily fit with in
the capillaries
White blood cell -
phagocyte
To defend the body against pathogens by
phagocytosis
Identified by a lobed/twisted nucleus

14. P a g e 14 | 22
White blood cell –
lymphocyte
To defend the body against pathogens by the
production of antibodies
Identified by a large round
How antibodies work
- Causes the pathogens to clump
together preventing reproduction
- Tags the pathogen so that phagocytes
may know to engulf them
- Neutralizes toxins produced by the
pathogens i.e. antitoxins
Nerve cell –
motor neuron
To transfer electrical signals throughout the
body
- Finger like projections called dendrites
to receive electrical signals
- Long axon to conduct the electrical
signal
- Myelin sheath to insulate the electrical
signal and allow for faster conduction
Muscle cell To contract and relax to bring about
movement in the body
- Has contractible fibers that allows the
cell to contract and relax
- Contains many mitochondria to
produce energy

15. P a g e 15 | 22
Plant
Specialized Cell
Structure Function and adaptation
Palisade cell To carry out photosynthesis in leaf
- Contains many chloroplast to
capture the sunlight, a
requirement for photosynthesis
- Contain a large vacuole that
pushes the chloroplast to the
perimeter of cell so that they may
have maximum exposure to the
light
Guard cell To open and close the stomata allowing
gas exchange and controlling water loss
within the leaf
In bright light the guard cells take in water
by osmosis and become plump and turgid.
In low light the guard cells lose water and
become flaccid, causing the stomata to
close.
Root hair cell To absorb minerals and water from the
soil
- Finger like projection that sticks
out into the soil to absorb water
and minerals
- Large vacuole to increase surface
area for maximum absorption of
water
Xylem To transport water
- Thick cell wall made of lignin to
support the water carried by the
xylem
- No end walls to allow water to
move from one xylem cell to the
next without obstruction
- No cytoplasm so water can move
without obstruction
Phloem To transport food (sucrose)
- Sieve plate has perforations that
allow food to move from one
phloem cell to the next
- Has a companion cell that
supplies the energy to move
substances via active transport

16. P a g e 16 | 22
6. Effects of climate change
Definition:
Climate change is the significant changes in the global weather patterns. It is the result of the
excessive emission of greenhouse gasses that absorb the suns energy and prevent it from
escaping the Earth’s atmosphere.
With the increase of the greenhouse gases in the atmosphere there is also the increase of
the amount of radiation retuning to the Earth's. As the temperature of the earth
increases climate zones and weather patterns will be disrupted

17. P a g e 17 | 22
a. Conservation of the environment
Definition:
CONSERVATION INVOLVES THE CAREFUL UTILIZATION OF A NATURAL
RESOURCES IN ORDER TO PREVENT ITS DEPLETION. Conservation means saving for the
future.
Importance:
Environmental conservation protects wildlife and promotes biodiversity. Maintaining a
healthy and functional ecosystem helps prevent the extinction of certain animal species.
If the environment is destroyed, some animals are forced out of their habitat, making it
hard for them to survive.
Different ways to conserve the environment:
▪ Passing laws to protect the environment and putting penalties in place to
discourage unsustainable practices
▪ Limit the use of fossil fuels and substitute with renewable energy sources
▪ Using public transport/carpooling/ reduce the amount if times you drive
(walking/riding the bicycle) to decrease the number of vehicles on the road thus
limiting the amount of car exhaust released in the atmosphere
▪ Turning of lights when not in use, or switching incandescent lights that use more
energy for fluorescent ones which are more energy efficient
▪ Reduce, reuse, and recycle your waste to prevent pollution and avoid health
hazards
▪ Educating the public about the benefits if conserving the environment to
influence their way of thinking to care more about the environment and so
encourage them to live more sustainable
▪

18. P a g e 18 | 22
7. Blood components: Sickle Cell Anemia, Genetic Diagram
Remember how to do a punnet square
Visual learners: https://www.youtube.com/watch?v=agQpPPQ5IVQ
o Need to know what the following terms mean
▪ Dominant recessive relationship
▪ Homozygous dominant
▪ Homozygous recessive
▪ Heterozygous
▪ Genotype
▪ Phenotype
o Example of a punnet square showing two heterozygous parents:

19. P a g e 19 | 22
8. Menstrual Cycle, Birth Control, STIs
KNOW HOW TO READ THESE GRAPHS
FSH: Follicle stimulating hormone matures the egg, and causes the release of estrogen
LH: Luteinizing hormone: responsible for ovulation and hence the creation of the corpus
luteum which produces progesterone
Estrogen: builds up the endometrium lining (rising levels of estrogen feedback negatively,
reducing the production and release of FSH from the pituitary)
Progesterone: builds maintains the lining
Stages of the menstrual cycle
Day 1 – 4/5 :
Day 1 of the cycle is the first day of a woman’s period. This is when the endometrium
lining starts to shed, this is what we call a period. Since the lining is shedding
progesterone and estrogen levels are low.
NOTE: FSH is being produce
Day 5/6-14:
After a woman’s period, she needs to prepare for the possibility of becoming pregnant
and so FSH stimulates the ovaries to release more estrogen. Estrogen levels begin to rise
to build back up the endometrium lining.
Day 14-25:
At the peak of estrogen (highest amount), there is a sudden release of LH from the
pituitary. This LH peak triggers the release of the matured egg, this is called ovulation.
After ovulation and the disruption of the follicle, this leaves behind the corpus luteum.
This is where progesterone is produced.

20. P a g e 20 | 22
Progesterone stimulates the uterus lining to thicken even more and maintains the lining.
In the event that the fertilization occurs, progesterone will continue to be produced to
ensure the endometrium lining stays.
High amounts of progesterone cause low amounts of estrogen to be produced
Day 25- 28
If no implantation occurs the hormonal changes start to occur. The corpus luteum
degenerates and so there is a decrease in progesterone.
BOTH ESTROGEN AND PROGGESTERONE LEVELS ARE LOW
Day 1
Low amounts of progesterone and estrogen causes the lining to shed, the unfertilized
egg is passed out via menstruation.
Birth Control
Definition:
Birth control also known as contraception is any method used to prevent pregnancy. There are four
main methods of contraception
1) Natural: the use of no chemicals/ devices
a. Calendar method: having sex during safe periods, at the stage of the menstrual cycle
where the woman is not ovulating
b. Abstinence: not having sex
c. Withdrawal method: taking the penis from the vagina before ejaculation
2) Barrier: prevents the sperm from meeting the egg
a. Use of condoms, male or female
b. Use of the diaphragm along with spermicide
c. IUD
3) Hormonal/Chemical : interferes with the hormone production to prevent ovulation
a. Birth control pills
4) Surgical/ Sterilization
a. Vasectomy: cutting and tying the vas deferens
b. Tubal ligation: cutting and tying the fallopian tubes

21. P a g e 21 | 22
STI: sexually transmitted infections
Definitions:
Sexually transmitted infections are a type pf pathogenic infection that may pass from person to person
by sexual activity.
Examples:
Gonorrhea, syphilis and AIDS (Acquired Immune Deficiency Syndrome)
AIDS
AIDS is caused by the virus called HUMAN IMMUNODEFICIENCY VIRUS (HIV). HIV attacks the
lymphocytes which play an important part in the body’s defense against disease. HIV, the virus can
change its antigen so that the body cannot identify and kill it. HIV starts to kill the white blood cells and
thus weaken the immune system. Opportunities disease such as tuberculosis, that our bodies would
normally fight against, can now strive on this weakened immune system. A person is diagnosed with
AIDS at the last stage of the diseases when their white blood cell count is extremely low.

22. P a g e 22 | 22