Photosynthesis, Respiration, Cell Types & Mendel’s Laws
Photosynthesis
Light-Dependent Reactions
Chlorophyll, the pigment giving plants their green color, resides within the thylakoid membranes of chloroplasts. This pigment captures light energy, exciting electrons in its molecules. This triggers a series of reactions, including the photolysis of water. Oxygen is released into the atmosphere, and hydrogen atoms are captured by organic molecules like NADP+, which becomes NADPH (used in the dark phase).
Dark Reactions (Calvin Cycle)
Occurring in the chloroplast stroma, these reactions utilize CO2. Hydrogen from NADPH and energy from ATP (produced in the light phase) drive a series of reactions, starting with CO2 and resulting in sugar synthesis. The final product, glucose, is later transformed into more complex sugars.
Respiration
Respiration releases the chemical energy stored in glucose.
Cellular Respiration
Taking place in mitochondria, cellular respiration involves the breakdown of glucose. Hydrogen atoms combine with oxygen to form water, carbon atoms form CO2, and the released energy is stored as ATP.
Glycolysis
The first stage, occurring in the cytoplasm, splits glucose into two molecules of pyruvic acid, releasing energy for ATP synthesis.
Krebs Cycle
The second stage. Pyruvic acid is split to yield acetic acid, which initiates a series of reactions in the mitochondria. Acetic acid combines with oxaloacetic acid to form citric acid. This loses a CO2 molecule, leading to alpha-ketoglutaric acid, which also loses CO2, becoming succinic acid. This converts to fumaric acid, then to malic acid, and finally back to oxaloacetic acid, restarting the cycle.
Photosynthesis vs. Respiration
| Photosynthesis | Respiration |
|---|---|
| Occurs only in green plants | Occurs in plants and other living organisms |
| Forms ATP | Releases ATP from glucose |
| Uses light, H2O, and CO2 to synthesize glucose | Releases H2O and CO2 |
| Releases oxygen | Consumes oxygen |
Types of Cells
- Epithelial Tissue: Covering and protection.
- Connective Tissue: Composed of stellate cells; connects and supports other tissues, fills spaces between organs, and protects delicate organs.
- Nervous Tissue: Formed by neurons (cell body and branches); conducts nerve impulses.
- Muscle Tissue: Long protein fibers; smooth, striated, and cardiac types. Striated: body movement; Smooth: organ function; Cardiac: heart contractions.
- Blood Tissue: Cells (white blood cells, platelets, red blood cells) suspended in plasma.
- Bone Tissue: Hard, resistant tissue; muscle attachment.
- Cartilage Tissue: Strong and elastic; provides flexibility for joints.
- Adipose Tissue: Large fat vacuoles; thermal insulation, fat reserve, protection from bumps.
Mendel’s Laws
Mendel’s First Law (Law of Segregation)
When crossing two purebred organisms differing in one trait, the F1 generation exhibits only the dominant trait. The recessive trait reappears in the F2 generation.
Mendel’s Second Law (Law of Independent Assortment)
When crossing organisms differing in two or more traits, each trait is inherited independently of the others.