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1. CYCLES IN NATURE -
PHOTOSYNTHESIS
First quarter: LIFE SCIENCE
SCI 8

2. 2. Photorespiration
-a process that happens in
plants when there's too
much oxygen (O₂) and not
enough carbon dioxide (CO₂)
inside the leaves.

3. ✓ The plant goes through
photorespiration instead
of normal
photosynthesis.
✓ Instead of making sugar,
it wastes energy and
loses carbon.
✓ This usually happens
when it's very hot or dry,
and the plant closes its
stomata (leaf pores) to
save water — which
reduces CO₂ levels.

4. ✓ What Does
Chlorophyll Do?
✓ It absorbs sunlight,
especially red and blue
light.
✓ It uses that sunlight
energy to help the plant
turn carbon dioxide and
water into sugar (food)
and oxygen.
✓ Think of chlorophyll like a
solar panel for the plant
— it collects light energy!
Fun Fact:
✓ Without chlorophyll, plants can’t do
photosynthesis.
✓ That's why it’s essential for plant survival — and
for us too, because it helps produce the oxygen we
breathe.

5. Lesson purpose
Plants are essential because they provide oxygen, absorb
harmful carbon dioxide, and help regulate the climate and
water cycle. They are the main source of food and shelter
for humans and animals, and they support biodiversity by
attracting pollinators. Additionally, plants offer medicinal
benefits, reduce stress, and contribute to culture and
livelihoods. Taking care of plants means caring for life, the
environment, and our own well-being.

6. NOTE: A chloroplast is a special part of a plant
cell where photosynthesis happens. It’s like a
tiny food factory inside the leaf

11. Leaves produce food for the plant
by a process called photosynthesis.
Photosynthesis produces glucose
and oxygen from carbon dioxide
and water, using light energy.

12. • Leaves have a large surface area to maximize light
absorption
• Leaves are thin, so there is a short distance for carbon
dioxide to diffuse into leaf cells
• Some cells in the plant leaves contain chloroplasts to
facilitate photosynthesis
• Leaves contain tiny holes called stomata to help with gas
exchange

14. This is a waxy substance
covering the upper
epidermis. It protects the leaf
from dehydration.

15. This protects the leaf
and it has no
chloroplast.

16. This is a cell
containing
chloroplast.

17. This cell organelle
contains chlorophyll.

18. A type of vascular tissue in
plants that is primarily
responsible for the
transport of water and
dissolved minerals from the
roots to the rest of the
plant.
Xylem

19. A type of vascular tissue in
plants responsible for the
transport of organic nutrients,
particularly the sugars produced
through photosynthesis, from
the leaves to other parts of the
plant.
Phloem

20. A pair of specialized cells surrounding each
stomata, responsible for opening and closing
the pore.
What are they?
By changing their shape (inflating or
deflating), guard cells control the size of the
stomata opening, regulating gas exchange
and water loss.
What’s their function?
Guard Cells

21. Microscopic pores on the leaf surface, allow for
gas exchange (carbon dioxide intake and
oxygen release).
What are they?
Controlled by guard cells, stomata open and
close to regulate gas exchange and water
loss.
What’s their function?
Stomata

22. • Carbon dioxide moves from the air
into the leaf through the stomata
• At the same time, oxygen moves out
of the leaf through the stomata
• Water vapour also diffuses out of
the stomata

23. The spongy mesophyll are packed
loosely, with air gaps in between
them for efficient gas exchange.
They are covered by a thin layer of
water, so gases can dissolve in the
water to move into and out of the
cells.

24. The lower epidermis is on the
underside of the leaf. It
contains tiny pores called
stomata.

25. Photosynthesis is the process of
making or putting together some
substances using light energy.
What is Photosynthesis?
Photo
– means light
Synthesis
– means putting together

27. Photosynthesis is the process by which plants make food using sunlight, carbon
dioxide, and water. Its efficiency depends on several factors:
Light Intensity
o More light = more photosynthesis (up to a certain point).
o Too little light slows or stops the process.
Carbon Dioxide (CO₂) Concentration
o More CO₂ = faster photosynthesis (up to a limit).
o CO₂ is a raw material in making glucose.
Temperature
o Moderate temperatures help enzymes work well.
o Too hot or too cold = enzymes slow down or get damaged.
Water Availability
o Water is a raw material in photosynthesis.
o Lack of water closes stomata and slows the process.
Chlorophyll
o More chlorophyll = more light absorbed.
o Yellowing or damaged leaves have less chlorophyll, so photosynthesis slows

28. Factors Affecting Respiration (in cells)
Respiration is how cells break down glucose to release energy. It also
depends on several conditions:
1.Glucose Availability
1.More glucose = more fuel for energy production.
2.Oxygen (for aerobic respiration)
1.Oxygen is needed to release large amounts of energy.
2.Lack of oxygen leads to anaerobic respiration (less efficient).
3.Temperature
1.Enzymes involved in respiration work best at moderate
temperatures.
2.Too hot or too cold = slower reaction or enzyme damage.
4.Cell Type and Activity
1.Active cells (like muscle cells) need more energy = more
respiration.

29. Why are leaves green?
Leaves are green because they contain a pigment called chlorophyll.
Chlorophyll absorbs light energy from the sun—mainly blue and red wavelengths.
It reflects green light, which is why leaves look green to our eyes.

32. WATER CYCLE
✓ The continuous movement of water through the
atmosphere, land, and bodies of water is called the
Water Cycle, which is also called the hydrological
cycle.
✓ The water cycle comprises different processes:
evaporation, condensation, precipitation,
transpiration, surface runoff, and infiltration.

33. https://www.teachengineering.org/curricularunits/view/cub_water_cycle_unit
✓ 90% of water vapor came from evaporation of water
from big
bodies of water like oceans, lakes and rivers.
✓ When animals exhale, they release water vapor

34. OXYGEN-CARBON DIOXIDE CYCLE
In the ecosystem, organisms consume
and produce oxygen and carbon dioxide
during the process of photosynthesis
and respiration. These important gases
flows through the organisms and the
environment through a cyclic process
called oxygen-carbon dioxide cycle

35. Water is absorbed by the roots and
passes through vessels in the stem on its
way to the leaves.
Carbon dioxide from the air passes
through small pores in the leaves. These
pores are called stomata.
Sunlight is absorbed by a green chemical
called chlorophyll. Sun’s energy is used
to split water molecules into hydrogen
and oxygen.
Hydrogen and carbon dioxide are used
to form glucose or food for plants.
THE PROCESS OF PHOTOSYNTHESIS

36. RESPIRATION
✓ All animals need oxygen to survive. They take in oxygen and
give off carbon dioxide through the process called
respiration.
✓ Animals get energy from the food they eat. During
respiration, cells use oxygen to break down sugar to obtain
energy.
✓ Animals use this energy to grow, reproduce, and to perform
other functions.
✓ They give off carbon dioxide into the atmosphere which in
turn is used by the plants during photosynthesis.

37. ✓ Photosynthesis occurs in the chloroplasts of plant cells and
stores energy in glucose.
✓ respiration occurs in the mitochondria of both plant and
animal cells and releases energy from glucose.
✓ These two processes are interdependent, forming a cycle
that supports life on Earth.