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1. Lamina = 🌱Section of a leaf which is wide and flat with large surface area for absorption of sunlight.

2. Petiole = 🌱Section of a leaf that joins lamina to the stem of a plant.

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1. ☘️ Cuticle

🟢it's a waxy and waterproof. Its transparent which allows sunlight to pass through it.

2. ☘️Upper Epidermis

🟢located at the upper surface of the leaf "under the cuticle".

🟢It's transparent so the light can pass through it

🟢this layer does not contain chloroplast.

3. ☘️Lower Epidermis

🟢located at the lower surface of the plant.

🟢this layer consists of stomata

🟢each stomata is guarded by a pair of guard cells

4. ☘️Palisade Mesophyll

🟢arranged vertically and closely packed to receive max light exposure.

🟢the cells are the sites for photosynthesis

🟢contains a lot of chloroplasts

5. ☘️Spongy Mesophyll

🟢Irregular shaped of cells which contains chloroplasts.

🟢Loosely arrangement of spongy mesophyll cells

🟢has less number of chloroplasts than palisade mesophyll

6. ☘️Vascular Bundle

🟢Xylem = -transports water and mineral salts -xylem walls are lignified and thickened to provide mechanical support to the plants.

🟢Phloem = -transports organic substances

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The Effect of Water Deficiency in Plants on Stomatal Opening and Closing

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The Effect of Water Deficiency in Plants on Stomatal Opening and Closing

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*with mild water deficiency

plants are usually slow-growing and stunted

Some plant leaves turn from shiny to dull at first signs of stress

Grasses which are the first to show the loss of water in the landscape will show signs of wilt.

1. Fresh Plants

➰when plants has enough water

➰guard cells becomes turgid

➰inner cell wall of the guard cell is thick and less elastic compared to the outer cell wall

➰think and more elastic cell wall causes the guard cells to curve outwards

➰the stoma opens

2. Wilted Plants

➰plants lack of water

➰guard cells become flaccid

➰thin and more elastic outer cell wall causes the guard cells to lose turgidity

➰the stoma closes

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The Mechanism of Stomatal Opening and Closing

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The Mechanism of Stomatal Opening and Closing

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Opening and Closing of the Stoma

🩵SUCROSE

❣️in the absence of light, photosynthesis does not ❌ occurs

❣️the sucrose concentration in the guard cells ⬇️ decreases

❣️water potential ⬆️ increases

❣️water molecules diffuses out from guard cells to epidermal cells via osmosis

❣️guard cells becomes turgid

❣️stoma closes I

❣️in the presence of light, photosynthesis ✅ occurs

❣️the concentration of sucrose in guard cells ⬆️ increases

❣️water potential ⬇️ decreases

❣️water molecules from epidermal cells to the guard cells via osmosis

❣️guard cells becomes turgid

❣️stoma opens

🩵POTASSIUM IONS

❣️potassium ions move out from guard cells

❣️solute potential in the guard cells ⬇️ decreases

❣️water potential in the ground ⬆️ increases

❣️water molecules diffuse out from the guard cells to epidermal cells via osmosis

❣️guard cells become flaccid

❣️stoma closes

❣️potassium ions enter the guard cells

❣️solute potential in guard cells ⬆️ increases

❣️water potential in the guard cells ⬇️ decreases

❣️water molecules from the epidermal cells diffuse to guard cells via osmosis

❣️guard cells become turgid

❣️stoma opens

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📗In the presence of light during daytime, photosynthesis ✅ occurs in guard cells.

📗glucose is produced and energy is generated for active transport

📗potassium ion is pumped into guard cells from the surrounding epidermal cells by active transport

📗this causes a reduction of water potential in the guard cells

📗water diffuses into guard cells by osmosis

📗guard cells become turgid

📗the guard cells curve outwards

📗the stoma opens

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📕at night, photosynthesis does ❌ not occur in guard cells

📕glucose is not ❌ produced and active transport does not occur in guard cells

📕potassium ions diffuses out from guard cells into the surrounding epidermal cells

📕water potential in the guard cells increases

📕water diffuses out from guard cells by via osmosis

📕guard cells becomes more flaccid

📕guard cells are less curvy

📕the stoma closes

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plants obtain essential gasses through leaves

plants need oxygen for respiration

plants need carbon dioxide for photosynthesis

During hot and dry weather, a plant loses a lot of water through transpiration.

this causes the guard cells to lose their turgidity which in turn causes the stomata to close

closing the stomata is to prevent the plant from losing excessive amount of water

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🧪transpiration is a process which water is lost from plant to the environment

🧪water is lost in the form of water vapour through the stoma and lenticels of plants

🦠Why does Transpiration rate increases ?

it increases when...

🧪increases in light intensity

🧪increases in temperature

🧪increases in air movement

🧪decreases in air humidity

🦠Why is Transpiration required in Plants?

🧪plant roots absorb water and mineral salts from soil

🧪water absorbs heat energy from leaves

🧪then evaporates as water vapour to give a cooling effect

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🏝roots absorb water from the soil

🏝The xylem transports water upwards in the plant stem

🏝leaf veins transport water to the leaves

🏝water evaporates to the atmosphere through stomata

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💜the relative air humidity is inversely proportional to the transpiration rate

💜the lower the air humidity of the surrounding atmosphere, the faster the water vapour escapes from the stomata

💜thus, the rate of transpiration becomes higher

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💙increase in temperature, will increase the kinetic energy of water molecules

💙thus, increasing the rate of transpiration

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🧡the higher the light intensity, the higher the rate of transpiration

🧡if the light intensity increases, the rate of transpiration will also increase.

🧡it will increase until it becomes constant

🧡The reason why the rate of transpiration is constant is because the

-🎾relative air humidity,

-🎾 temperature

-🎾air movement

🧡the air movement becomes the limiting factors

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💚the faster the air movement, the faster the rate of transpiration

💚the wind speed is directly proportional to the transpiration rate

💚the movement of air carries away water molecules that have been diffused out from the leaves

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The Necessity of Photosynthesis in Plants

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The Necessity of Photosynthesis in Plants

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❇️The photosynthetic product is glucose, the primary source for cellular transpiration used to synthesize energy

❇️The glucose produced can be used to from cellulose

❇️The glucose produced can be converted into sucrose and transported to other parts of plant for metabolism or storage in the form of starch

❇️Glucose can be converted into amino acids, proteins, fats for metabolism or storage

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Brief History of Discovery of Photosynthesis 

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Brief History of Discovery of Photosynthesis 

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⭐️ In 1640, Jan-Baptisa van Helmont carried out an experiment to test the idea that plants obtained their food from soil.

Seedling weighed 2.3kg ➡️ 90 kg of dried soil ➡️ Plant was watered for 5 years ➡️ Plant weighed 77kg ➡️ 90kg of dried soil

📌 Helmont’s conclusion :

The plant had grown by only being watered and not from the water of the soil

⭐️ In the year 1772, an experiment conducted by Joseph Priestly showed that plants released oxygen to the atmosphere

➡️ A rat was placed in an inverted glass jar .

The rat died.

➡️ A rat was placed in an inverted glass jar with a plant, the rat lived.

📌 Priestly’s conclusion :

Plants release oxygen.

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The Adaptation of the Internal Structure of a Leaf to Photosynthesis 

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The Adaptation of the Internal Structure of a Leaf to Photosynthesis 

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UPPER EPIDERMIS AND LOWER EPIDERMIS

⭐️ Transparent waxy cuticle (on upper and lower epidermis)

• 🔅Allows sunlight to penetrate the upper and lower epidermis into the palisade mesophyll

⭐️ Stomata (present in lower epidermis)

🔅Pore that formed from two guard cells

🔅For gaseous exchange and transpiration

PALISADE MESOPHYLL

🔅Cells which have abundant of chloroplasts-can carry out photosynthesis

🔅Cylindrical shape of cells-more cells can be arranged compactly

🔅Cells arranged compactly absorb sunlight maximally for photosynthesis

SPONGY MESOPHYLL

🔅Cells which have chloroplasts-can carry out photosynthesis

🔅Irregular shaped of cells and loosely arranged-to form air spaces for transpiration and gaseous exchange

VASCULAR BUNDLES

⭐️ Xylem

🔅Transport water and mineral salts from roots to mesophyll for photosynthesis

⭐️ Phloem

🔅Transport organic products from leaves to other parts of plants

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✨THYLAKOID

• 🫧Disk-shaped sacs containing chlorophyll

• 🫧Photosynthesis pigments are present to trap sunlight

• 🫧Where light-dependent reaction occurs

✨GRANUM

•🫧 A disk-shaped stack of thylakoids

• 🫧The arrangement increases the surface area for optimal photosynthesis

✨STROMA

• 🫧Colourless fluid surrounding granum in the chloroplast

• 🫧Site for light-independent reaction to take place which produces glucose

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🍃this is the first stage called the light-dependent where it produces oxygen and water molecules

🍃the light-dependant reactions occurs in the thylakoid

🍃thylakoid is a membrane

🍃During the light-dependant reactions, photosynthetic pigments on the surface of thylakoid absorb light energy

🍃Light energy is used to excite electrons in the chlorophyll pigment to a higher level

🍃the excited electrons will finally be accepted by the final electron carrier, namely NADP+

🍃simultaneously, light energy will also be used to breakdown water molecule to hygrogen ions (H+) and hydroxyl ions (OH-) by photolysis of water

🍃NADP+ combines with hydrogen ions to form NADPH

🍃hydroxyl ion loses an electron to form oxygen and water

🍃the products of light-independent reactions are ATP, NADPH, and oxygen.

🍃ATP and NADPH then enter the light-independant reactions, whereas oxygen is released to the atmosphere.

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🍃the second stage is called light-independent reactions

🍃The light-independent reactions occur in stroma

🍃during the light-independent reactions, carbon dioxide binds to the 5-carbon organic compound

🍃NADPH and ATP produced from the light-dependent reactions reduce the 6-carbon organic compound to a glucose monomer

🍃glucose monomer is then condensed to form starch molecule which is kept in the stroma as granules

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The overall reactions of Photosynthesis can be represented in the following equation:

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The overall reactions of Photosynthesis can be represented in the following equation:

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🌙Both occur in chloroplast

🌙Both are catalysed by enzymes

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💌carbon dioxide is needed to synthesize glucose in light-independent reactions

💌as the carbon dioxide increases, the photosynthesis rate increases until it reaches saturation point

💌after the saturation point, increases in the concentration of carbon dioxide no longer increase the rate of photosynthesis

💌limiting factors such as light intensity and temperature limit the increase in photosynthesis rate after the saturation point

💌photosynthesis rate can be increased by increasing light intensity

💌however, if the light intensity is too high, the stomata will close to reduce the water loss through transpiration. This prevents carbon dioxide from entering the leaf, which subsequently decreases photosynthesis rate

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💌Light energy is needed for light photolysis and to activate chlorophyll in light-dependent reactions

💌as light intensity increases, the photosynthesis rate increases until it reaches the saturation level at point P (Graph (i))

💌after point P, the increase in light intensity no longer causes the increase in the photosynthesis rate

💌limiting factors such as carbon dioxide and temperature had limited the increase of photosynthesis rate

💌photosynthesis rate can be increased by increasing concentration of carbon dioxide or temperature (graph (ii))

💌when light intensity is too high, photosynthesis rate slows down because chlorophyll pigments are damaged by ultraviolet rays

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💌any changes in temperature will affect the photosynthesis rate because light-independent reactions are catalysed by enzymes

💌as the temperature increases, the rate of photosynthesis will also increase until the optimum temperature. The optimum temperature of most plants is between 25°C to 30°C

💌at higher temperature than the optimum temperature, photosynthesis rate decreases because the enzymes are denatured

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The compensation point is the level of light intensity at which the rate of photosynthesis is equal to the rate of respiration

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The compensation point is the level of light intensity at which the rate of photosynthesis is equal to the rate of respiration

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The Similarities between Photosynthesis and Respiration in Plants

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The Similarities between Photosynthesis and Respiration in Plants

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💐Both processes take place in living organisms

💐Both processes involve the uptake and release of gases

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The Differences between Photosynthesis and Respiration in Plants

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The Differences between Photosynthesis and Respiration in Plants

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💥Photosynthesis

🪸the organism involved is only green plant

🪸it occurs in the presence of light

🪸the substance needed is water and carbon dioxide

🪸the product is glucose and oxygen

🪸the site of the process is at chloroplast

🪸the energy conversation is light energy to chemical energy

🪸the aim is to synthesise glucose and organic compounds in plants

🪸the type of metabolism is anabolism

💥Respiration

🪸the organism involved is all living organism

🪸it occurs all the time

🪸the substance needed is glucose and oxygen

🪸the product is carbon dioxide, water, and energy

🪸the site of the process is at the mitochondrion

🪸the energy conversation is chemical energy is converted to ATP and heat is released

🪸the aim is to generate energy for metabolic activites

🪸the type of metabolism is catabolism

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The Differences between Light-dependent and Light-independent reactions

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The Differences between Light-dependent and Light-independent reactions

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💡Light-dependant

🎉The reaction site is at thylakoid

🎉The substance required is water

🎉the products of the reactions is oxygen and water

🎉involve photolysis of water

🎉doesn't involve the reduction of carbon dioxide

🎉it produces ATP molecules

💡Light-independent

🎉the reaction site is at the stroma

🎉the substances required is carbon dioxide

🎉the product of the reactions is glucose

🎉Doesn't involve photolysis of water

🎉involve the reduction of carbon dioxide

🎉it uses ATP molecules

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The Effect of Different Light Intensities and Light Colours on the Rate of Photosynthesis

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The Effect of Different Light Intensities and Light Colours on the Rate of Photosynthesis

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🌈light colours play and important role in photosynthesis

🌈Light spectrum consist of seven colours in a certain sequence which is violet, indigo, blue, green, yellow, orange and red.

🌈each colour has a different wavelength

🌈Plants only use a few types of light colours in photosynthesis

🌈photosynthesis rate is highest in blue light, followed by red light

🌈all of red light is absorbed by chlorophyll

🌈the blue light is absorbed by carotenoid pigments before being transferred to the chlorophyll

🌈these two lights have enough amount of energy to excite electrons in the light-dependent reaction

🌈green light is not absorbed by plants, therefore green light is not used in photosynthesis