Comprehensive Study Notes: Cellular Respiration, Photosynthesis, Plant Transport, Animal Physiology, and Population Ecology

Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells convert the chemical energy stored in glucose into adenosine triphosphate (ATP), a more usable form of energy. This process involves a series of redox reactions where electrons move from less electronegative to more electronegative molecules. Cellular respiration includes both anaerobic and aerobic stages.

• Anaerobic stage: Glycolysis (produces 2 ATP)

• Aerobic stages: Pyruvate oxidation, Citric Acid Cycle (Krebs Cycle), and Oxidative Phosphorylation (produces 34-36 ATP)

Key Equations:

• Overall reaction: $\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP}$

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which light energy is converted into chemical energy, forming covalent bonds in organic molecules. Electrons move from more electronegative to less electronegative molecules. The process is divided into two main stages:

• Light-dependent reactions: Light energy is used to produce ATP and NADPH.

• Calvin Cycle: Carbon atoms from CO2 are fixed to build three-carbon sugars using the enzyme rubisco (in C3 plants).

Key Equation:

• $\mathrm{6CO_2 + 6H_2O + light \rightarrow C_6H_{12}O_6 + 6O_2}$

Alternatives to the C3 Pathway

Rubisco, the enzyme responsible for carbon fixation in the Calvin Cycle, can sometimes fix O2 instead of CO2, leading to energy waste (photorespiration). Plants have evolved two alternative pathways to minimize this:

• C4 pathway: Separates carbon fixation and the Calvin Cycle into different cells (mesophyll and bundle sheath cells).

• CAM pathway: Separates carbon fixation and the Calvin Cycle in time (night and day).

• Both use PEP carboxylase, which does not bind O2.

Hemoglobin and Oxygen Transport

Hemoglobin Structure and Function

Hemoglobin is a protein in red blood cells that reversibly binds oxygen, allowing efficient oxygen transport in the blood. Each hemoglobin molecule has four oxygen binding sites. Hemoglobin is essential because water alone cannot carry sufficient oxygen in the blood.

• Hemoglobin adapts to different localized environments in the body, facilitating oxygen delivery where needed.

Key Concept: The oxygen-hemoglobin dissociation curve shows how hemoglobin's affinity for oxygen changes with partial pressure of oxygen (pO2).

Plant Transport Systems

Xylem and Phloem

Plants have two main vascular tissues for transport:

• Xylem: Transports water and minerals from roots to leaves; composed of dead cells.

• Phloem: Transports sugars and nutrients in all directions (mainly downward); composed of living cells.

Pathway of Water Movement in Roots

Water is absorbed into root cells by osmosis and moves through ground tissue via three routes:

• Symplastic transport: Through cytoplasms of adjacent cells via plasmodesmata.

• Apoplastic transport: Through cell walls of adjacent cells.

• Transmembrane transport: Alternates between symplastic and apoplastic pathways.

Casparian Strip

The Casparian strip is a waxy, water-impermeable barrier in the cell walls of endodermal root cells. It serves two main functions:

• Stops apoplastic transport at the endodermis.

• Forces water to enter the symplastic pathway, ensuring selective filtering by the plasma membrane.

Movement of Water in the Xylem

Water is pulled up the xylem primarily due to transpiration (evaporation of water from leaves). The process relies on:

• Cohesion: Water molecules stick together.

• Adhesion: Water molecules stick to xylem walls.

• Osmosis: Drives water into roots.

Transpiration and Tension

Transpiration causes water vapor to diffuse out of the leaf via stomata. Water evaporates from the xylem, creating negative pressure (tension) that pulls water upward from the roots to the leaves.

Animal Tissues and Organ Systems

Types of Animal Tissues

Animal bodies are organized into 11 organ systems, each composed of four main tissue types:

• Epithelial tissue: Lines body surfaces and internal organs.

• Connective tissue: Binds cells and organs together.

• Muscle tissue: Contracts to produce movement.

• Nervous tissue: Generates and propagates electrical signals.

Diffusion and Osmosis

Principles of Diffusion and Osmosis

Diffusion is the movement of solute particles from high to low concentration. Osmosis is the movement of water from low solute concentration to high solute concentration. Two important terms:

• Osmolarity: Number of solute particles in a solution.

• Tonicity: The effect of a solution on cell volume (shrink, expand, or stay the same).

Circulatory System

Blood Flow Through the Heart

The heart pumps blood through two circuits: pulmonary (to the lungs) and systemic (to the body). The pathway is as follows:

1. Deoxygenated blood enters the right atrium via the vena cava.

2. Blood flows to the right ventricle, then to the lungs via the pulmonary artery.

3. Oxygenated blood returns via the pulmonary vein to the left atrium.

4. Blood flows to the left ventricle, then is pumped to the body via the aorta.

Blood Vessels

There are three main types of blood vessels:

• Arteries: Carry blood away from the heart (oxygenated in systemic, deoxygenated in pulmonary circulation).

• Veins: Carry blood to the heart (deoxygenated in systemic, oxygenated in pulmonary circulation).

• Capillaries: Sites of gas exchange between blood and tissues.

Respiratory Systems

Gas Exchange in Mammals

Gas exchange occurs in the alveoli of the lungs. Oxygen dissolves in a thin water layer lining the alveoli and diffuses into the blood in capillaries. Efficient gas exchange is enhanced by counter-current systems, where air/water and blood flow in opposite directions, maximizing transfer.

Plant Sensory Systems

Phytochromes

Phytochromes are plant photoreceptors that detect red and far-red light, regulating growth and development. They exist in two forms:

• Pr: Absorbs red light, inhibits germination, stimulates vertical growth.

• Pfr: Absorbs far-red light, stimulates germination, inhibits vertical growth, stimulates horizontal growth.

Flowering and Photoperiodism

Flowering in plants is controlled by night length (photoperiod). Long-night (short-day) plants flower when nights exceed a critical length, while short-night (long-day) plants flower when nights are shorter than a critical period. Flashes of light can reset the flowering response.

Membrane Transport

Channel vs. Carrier Proteins

Facilitated diffusion allows molecules that are too large or charged to cross the membrane via proteins:

• Channel proteins: Form hydrophilic tunnels; open to both sides simultaneously.

• Carrier proteins: Change shape to move molecules; open to one side at a time; may require energy.

Population Ecology

Exponential vs. Logistic Growth

Population growth can be modeled in two main ways:

• Exponential growth: Occurs with unlimited resources; not sustainable long-term.

• Logistic growth: Accounts for carrying capacity (K), the maximum population size the environment can support.

Logistic Growth Equation:

• $\mathrm{\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)}$

Life Tables

Life tables summarize population dynamics:

• Survivorship (Lx): Fraction of population surviving to a certain age.

• Fecundity (mx): Number of offspring produced by an average organism of a certain age.

• Lxmx: Realized fecundity.

• Sum of all Lxmx values gives the net reproductive rate (R0):

• If R0 > 1, population is growing.

• If R0 < 1, population is shrinking.

Net Reproductive Rate Equation:

• $\mathrm{R_0 = \sum (L_x m_x)}$