Chapter 1 - Photosynthesis and the Carbon Cycle

●​ What is Photosynthesis?​
Photosynthesis is the process by which plants transform light energy into chemical
energy. During this process, light energy is captured by chlorophyll and used to convert
carbon dioxide, water, and minerals into glucose and oxygen. The glucose produced
can either be stored or used as an energy source through respiration.

●​ Photosynthesis Equations:​
Word Equation: Carbon dioxide + Water → Glucose + Oxygen​
Symbol Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

●​ Site of Photosynthesis:​
Photosynthesis takes place in the chloroplasts of plant cells. These organelles contain
chlorophyll, a green pigment that absorbs light energy and converts it into chemical
energy to produce carbohydrates.

●​ Factors Affecting Photosynthesis Rate:

Light Availability: Light provides the energy needed for photosynthesis. As the light
intensity increases, the rate of photosynthesis increases. However, if light intensity is
low, the rate of photosynthesis slows down.
Water Availability: Water is a raw material needed in photosynthesis. If there is not
enough water, the process slows down because the plant cannot produce glucose.
Severe water shortage can even stop photosynthesis completely.
Temperature: Photosynthesis is controlled by enzymes, which work best at an
optimum temperature (around 25°C for most plants). If the temperature is too low, the
 enzymes work slowly, reducing the rate of photosynthesis. If the temperature becomes
too high, the enzymes become denatured, stopping the process.
Carbon Dioxide Concentration: Carbon dioxide is another raw material needed for
photosynthesis. A higher carbon dioxide concentration increases the rate of
photosynthesis. However, if carbon dioxide levels are low, the rate of photosynthesis
decreases.

●​ Leaf Structure and Adaptations for Photosynthesis:

Chloroplast: A green organelle found in plant cells where photosynthesis takes place. It
uses sunlight to produce carbohydrates like glucose, which provide energy to the plant.
Chlorophyll: A green pigment inside the chloroplast that absorbs sunlight and helps in
making carbohydrates during photosynthesis.
Cuticle: A waxy outer layer that reduces water loss while allowing light to pass through.
Upper Epidermis: A transparent protective layer that allows sunlight to reach the inner
layers.
Palisade Mesophyll: Tightly packed cells that are rich in chloroplasts to absorb
maximum sunlight.
Spongy Mesophyll: Loosely arranged cells with air spaces to facilitate gas exchange.
Guard Cells and Stomata: Stomata allow carbon dioxide to enter and oxygen to leave.
Guard cells control the opening and closing of stomata to regulate water loss.
Xylem: Transports water and minerals from the roots to the leaves through
transpiration.
Phloem: Transports glucose and other nutrients throughout the plant via translocation.
 The leaf is adapted for photosynthesis by having a large surface area, thin structure,
and specialized cells to maximize light absorption and gas exchange.

●​ Minerals Essential for Plant Health:

Nitrate Ions: Needed for the production of amino acids, proteins, and enzymes.
Deficiency results in poor growth and yellow leaves.
Magnesium Ions: Essential for making chlorophyll. Lack of magnesium causes yellow
leaves and stunted growth.

●​ Importance for Farmers:​

Farmers can maximize crop yield by:
Using greenhouses to maintain optimum temperatures.
Installing artificial lighting to allow photosynthesis during the night.
Increasing carbon dioxide levels in greenhouses to boost the rate of photosynthesis.

●​ Why is Photosynthesis Important?

Oxygen Production: Releases oxygen needed by humans and animals for breathing.
Food Source: Produces glucose, which gives energy to plants and forms the base of the
food chain.
Gas Balance: Maintains the balance of oxygen and carbon dioxide in the atmosphere.
Energy Transfer: Supports life by transferring energy from plants to other living
organisms.

●​ Test for Starch:

The starch test is used to determine whether a variegated leaf has undergone
photosynthesis by checking for the presence of starch. To begin, a beaker of water is
heated on a tripod stand until it starts boiling. Once the water is boiling, the leaf is
dropped into it and left for about two minutes. Boiling the leaf kills it and breaks down
 the cell walls, making it easier for iodine to enter later in the experiment. After boiling,
the leaf is carefully removed and placed in a test tube filled with ethanol. This test tube
is then placed in a hot water bath to heat the ethanol, as direct heating is not used since
ethanol is flammable. Ethanol removes the chlorophyll from the leaf, turning it pale or
white, which makes the iodine test results clearer. Once the leaf has lost most of its
green color, it is taken out of the ethanol and dipped into warm water to soften it, as
ethanol makes the leaf brittle. The leaf is then placed on a white tile, and iodine solution
is added. If starch is present, the iodine turns blue-black, indicating that
photosynthesis has taken place. If no starch is present, the leaf remains
yellowish-brown or orange, the original color of iodine. In a leaf that has both green
and non-green areas, only the green parts turn blue-black, while the non-green areas
do not change color. This proves that chlorophyll is necessary for photosynthesis and
that starch is only produced in the parts of the leaf where photosynthesis occurs.

●​ What is the Carbon Cycle?​

The carbon cycle is the natural process by which carbon moves between the
atmosphere, plants, animals, soil, and oceans. It plays a key role in maintaining the
Earth's balance of carbon dioxide.

●​ Stages of the Carbon Cycle:

1.​ Photosynthesis: Plants absorb carbon dioxide from the air to produce glucose and
oxygen.
2.​ Respiration: Plants, animals, and humans release carbon dioxide back into the air
when they breathe.
3.​ Decomposition: When plants and animals die, decomposers break down their bodies,
releasing carbon dioxide into the atmosphere.
4.​ Combustion: Burning fossil fuels or wood releases stored carbon back into the air as
carbon dioxide.
5.​ Carbon in Oceans: Oceans absorb carbon dioxide from the air, where it dissolves into
water and is used by marine plants.
6.​ Formation of Fossil Fuels:
Over millions of years, dead plants and animals are buried under layers of soil and turn
into fossil fuels like coal, oil, and natural gas.

●​ Importance of the Carbon Cycle:

Maintains the balance of carbon dioxide in the atmosphere.
Provides carbon for plants to make food.
Helps regulate Earth's temperature.
 Chapter 4 - Maintaining life

●​ What are Root Hair Cells?

They are specialized cells found on the surface of plant roots that help absorb water
and minerals. These cells have long extensions that increase the surface area, making it
easier to absorb water and minerals from the soil. They absorb water and dissolved
minerals from the soil through osmosis and active transport.

●​ How Water Moves Up the Plant:

1.​ Osmosis: Water from the soil moves into root hair cells because there is more water in
the soil than inside the root cells.
2.​ Xylem Vessels: Water passes into thin tubes called xylem vessels, which carry water
from the roots to other parts of the plant.
3.​ Capillary Action: Water moves up the narrow xylem tubes because water molecules
stick to the tube walls (adhesion) and to each other (cohesion).
4.​ Transpiration Pull: Water evaporates from the leaves through tiny openings called
stomata. This creates a pull that draws more water up from the roots.
5.​ Continuous Flow: As long as water keeps evaporating from the leaves, water will
continue to move up through the plant.
●​ The structure and function of Xylem in plants:
Xylem is a tube-like tissue in plants that carries water and minerals from the roots to
the leaves and other parts of the plant. It is made of dead cells joined together, forming
long, hollow tubes. Xylem is found in the roots, stems, and leaves, alongside phloem in
vascular bundles. Its main function is to transport water and minerals to different parts
of the plant and provide support to help the plant stay upright.

●​ What is Transpiration?
Transpiration is the process by which water evaporates from the leaves of plants
through tiny openings called stomata. This process helps plants get rid of excess water
and plays an important role in the movement of water through the plant.
●​ Investigating Transpiration:
This experiment compares the rate of transpiration in two plants to show where water
loss happens more quickly. In the first plant, a plastic bag covers the leaves, leaving the
pot and soil exposed. In the second plant, the plastic bag covers only the pot and soil,
leaving the leaves uncovered. Over time, the mass of the second plant decreases more
than the first because transpiration occurs faster through the leaves than from the soil.
Leaves have more stomata, tiny openings that allow water vapor to escape. In contrast,
the first plant loses water more slowly, as the plastic bag traps moisture around the
leaves, reducing transpiration. Since soil loses water mainly through evaporation,
which is slower than transpiration, the second plant shows a greater and faster
decrease in mass, proving that transpiration happens mostly through the leaves.

●​ How Water Moves Through the Plant:

Water is first absorbed by the root hair cells from the soil through osmosis. It then
travels up the plant through the xylem vessels, which are hollow tubes made of dead
cells. When water reaches the leaves, it evaporates through the stomata. This
evaporation creates a pulling force called the transpiration pull, which helps draw more
water from the roots to the leaves.

●​ Why Do Plants Need Water?

Cooling: Water evaporates from the leaves, helping the plant cool down.
Photosynthesis: Water is used to produce glucose during photosynthesis.
Transport: Water helps transport minerals and glucose to different parts of the plant.
Turgidity: Water fills plant cells, making them firm and helping the plant maintain its
shape.
●​ What is Excretion?​
Excretion is the process by which living organisms remove waste products made by
their bodies. These waste products include substances like carbon dioxide( made by
body cells in respiration), urea( made in liver cells), and excess water(not needed by the
body), which need to be removed to keep the body healthy and prevent damage.

●​ Excreting Urea:​
Urea is a waste product made by the liver when it breaks down extra proteins. The
kidneys filter urea from the blood and mix it with water to form urine. The urine
travels from the kidneys through tubes called ureters to the bladder, where it is stored.
When the bladder is full, urine leaves the body through the urethra.

●​ Parts Involved in Excreting Urea:

Kidney: Filters urea, water, and other waste products from the blood to form urine.
Renal Artery: Carries oxygen-rich blood with waste materials to the kidneys.
Ureter: Thin tube that carries urine from the kidneys to the urinary bladder.
Urinary Bladder: Stores urine until it is ready to leave the body.
Urethra: Tube that carries urine out of the body from the bladder.
Renal System: The system made up of the kidneys, ureters, bladder, and urethra, which
helps in removing waste from the body.
 Chapter 7 - Genes and Inheritance

●​ Genetics and Inheritance:

Chromosomes: Chromosomes are thread-like structures found in the nucleus of a cell.
They are made of DNA and carry genetic information. Humans have 46 chromosomes
(23 pairs) in each cell.
DNA (Deoxyribonucleic Acid): DNA is a molecule that contains instructions for how
the body develops and functions. It carries the genetic code that determines traits. For
example, eye colour and height.
Genes: Genes are small sections of DNA found on chromosomes. Each gene controls a
specific characteristic, like hair colour or blood type.
Inheritance: Inheritance is the process by which traits are passed from parents to their
children through genes. Some characteristics, like eye colour and hair colour, are
inherited from both parents.

●​ What are Gametes?

Gametes are sex cells. In humans, the sperm cell is the male gamete and the egg cell
(ovum) is the female gamete. Gametes contain 23 chromosomes each, half the number
of normal body cells.

Egg Cell Sperm Cell

Female gamete Male gamete

Bigger Smaller

Cannot move by itself Swims using tail

Contains Food Does not contain Food

●​ Reproduction:
Fertilisation: Fertilisation happens when a sperm cell and an egg cell join together.
This forms a single cell called a zygote, which contains 46 chromosomes — half from
the mother and half from the father.
Boy or Girl: The sex of the baby is determined by the sperm cell. If the sperm carries
an X chromosome, the baby will be a girl (XX). If the sperm carries a Y chromosome, the
baby will be a boy (XY).

●​ What is Variation?
Variation is the differences between individuals of the same species. It can be caused by
DNA or environmental factors. Variation due to DNA happens when traits are passed
down from parents to offspring. This type of variation affects things like fur colour in
animals, flower colour in plants, or eye colour in humans. Variation due to the
environment happens because of external factors like food, climate, or living
conditions. For example, plants might grow taller if they get more sunlight, and animals
might have thicker fur if they live in colder places.

●​ Natural Selection:
In every species, there is variation among individual organisms. Some of this variation
is caused by differences in their genes. Certain individuals have advantageous features
that help them survive better than others. For example, giraffes with longer necks can
 reach more food. These individuals are more likely to survive and reproduce. When
they reproduce, they pass on the genes for these helpful features to their offspring.
Over many generations, the genes for advantageous features become more common,
while genes for less useful features become less common. This process of survival and
passing on helpful traits is called natural selection, and it helps species adapt to their
environment over time.

●​ Peppered Moth Example:

1.​ Variation: In the population of peppered moths, there were two types of moths –
light-coloured moths and dark-coloured moths. This difference in colour was due to
variation in their genes.
2.​ Natural Selection: Before the Industrial Revolution, the light-coloured moths could
blend with the light bark of trees, making them harder for birds to see. However, after
pollution made the trees darker, the dark-coloured moths were better camouflaged,
while light-coloured moths were more easily seen and eaten by predators.
3.​ Transfer of Genes: Since more dark-coloured moths survived, they were able to
reproduce and pass on their dark colour genes to their offspring.
4.​ Population Change: Over many generations, the number of dark-coloured moths
increased in the population, while the number of light-coloured moths decreased. This
shows how natural selection causes changes in a population over time.

●​ Bacteria and Antibiotics:

In a group of bacteria, there are small differences between individuals. Some bacteria
are naturally resistant to antibiotics because of their genes, while others are not. When
antibiotics are used, the bacteria that are not resistant die. The resistant bacteria
survive and reproduce, passing on their resistant genes to their offspring. Over time,
more bacteria in the population become resistant to antibiotics, making the infection
harder to treat.
●​ Extinction:
Extinction happens when no living members of a species are left. It can occur due to
natural causes like climate change, new predators, or diseases. Human activities such
as deforestation, pollution, and hunting also increase the risk of extinction. When a
species becomes extinct, it affects the balance of the ecosystem. An example is the
dodo, which became extinct because of hunting and the introduction of new animals.
Protecting habitats, creating national parks, banning hunting, and breeding endangered
animals in captivity can help prevent extinction.