Biology Notes for Grade 10

Light Reaction (Light-Dependent Stage):
- Location: Occurs in the grana (stacks of thylakoids) of chloroplasts, where chlorophyll and other pigments are embedded.
- Process: Involves Photosystems I and II and an Electron Transport System (ETS). Chlorophyll absorbs energy from sunlight (maximally at blue and red wavelengths).
- Photolysis: Light energy is used to split water (H{2}O) into hydrogen ions (H^{+}), electrons, and oxygen (O{2}). The oxygen is released as a byproduct.
- Photophosphorylation: Energy released during electron transport is used to synthesize ATP.
- Inputs: Light energy, water (H_{2}O), NADP, and ADP.
- Outputs: NADPH, ATP, and oxygen (O_{2}).
Dark Reaction (Light-Independent Stage / Calvin Cycle):
- Location: Occurs in the stroma of the chloroplast.
- Process: Utilizes ATP and NADPH from the light reactions. Carbon dioxide (CO_{2}) is fixed through a series of enzyme-controlled steps (Carbon Fixation).
- Inputs: CO_{2}, ATP, NADPH.
- Outputs: Glucose (C{6}H{12}O_{6}), ADP, and NADP.
Overall Chemical Equation:
- 6CO{2} + 6H{2}O + \text{sunlight/chlorophyll} \rightarrow C{6}H{12}O{6} + 6O{2}

Iodine Test Procedure:
1. Boil in water: Destroys the selective permeability of the cell membrane and kills the leaf.
2. Decolorize in ethanol: Removes chlorophyll by boiling the leaf in alcohol (using a water bath for safety) so color changes are visible.
3. Rinse in cold water: Softens the leaf which becomes brittle after ethanol treatment.
4. Stain with iodine: Spread the leaf on a white tile and add iodine solution.
Results:
- Positive: Blue-black color indicates the presence of starch (product of photosynthesis).
- Negative: Brown/yellow color indicates no starch is present.

Xylem: Conducts water and dissolved minerals from the roots to the leaves. It consists of dead cells like vessels and tracheids.
Phloem: Transports organic nutrients (sucrose, amino acids) from "sources" (leaves) to "sinks" (roots/fruits). It consists of living cells: sieve tube elements and companion cells.
Translocation: The energy-requiring process move substances through the phloem, often Explained by the Pressure-Flow Hypothesis.

Absorption: Water enters root hairs via osmosis (moving from high to low water potential), while minerals enter via diffusion or active transport.
Transpiration Pull: As water evaporates from stomata (transpiration), it creates a tension that pulls the water column upward through the xylem.
Cohesion and Adhesion: Cohesion (water molecules sticking to each other) and Adhesion (water molecules sticking to xylem walls) ensure a continuous water column.

Phototropism: Growth response to light. Shoots are positively phototropic (grow toward light), mediated by the hormone Auxin, which accumulates on the shaded side causing cell elongation.
Geotropism (Gravitropism): Response to gravity. Roots are positively geotropic (grow downward), while shoots are negatively geotropic.
Hydrotropism: Roots grow toward moisture sources.
Darwin's Experiment: Proved that the tip of the coleoptile senses light and transmits a signal (auxin) to the growth zone.

Teenadem (Ruta chalepensis): Used for treating abdominal pain and various stomach upsets.
Jinjibil (Zingiber officinale): Used for treating tonsillitis, common colds, and respiratory issues.
Ye-kosso Zaf (Hagenia abyssinica): A traditional remedy specifically for treating tapeworm infestations.

Inorganic Molecules: Simple molecules lacking carbon-hydrogen bonds, such as water (H_{2}O), salts, and minerals.
Organic Molecules: Complex carbon-based molecules including Carbohydrates (energy), Lipids (storage/membranes), Proteins (structure/enzymes), and Nucleic Acids (genetic info).
Properties of Water:
- High Specific Heat: Helps maintain stable temperatures.
- High Latent Heat of Vaporization: Provides cooling through sweating/transpiration.
- Solvent Properties: Dissolves polar and ionic substances for transport.