General Biology: Metabolism, Digestion, Respiration, Cell Division, Photosynthesis, and Reproduction

Metabolism and Digestion

Types of Metabolism

Metabolism refers to all chemical reactions that occur within living organisms to maintain life. Organisms obtain energy and carbon through various metabolic strategies.

• Autotrophs (Producers): Obtain carbon from carbon dioxide (CO2). Examples: Plants, some bacteria, some protists.

• Heterotrophs (Consumers): Obtain carbon from organic compounds (carbohydrates, lipids, proteins). Examples: Animals, most bacteria, fungi, some protists, archaea.

• Phototrophs: Obtain energy from light.

• Chemotrophs: Obtain energy from external chemical compounds (organic or inorganic).

  • Organic: Carbohydrates, triglycerides, proteins.

  • Inorganic: Hydrogen sulfide, hydrogen, sulfur, iron, ammonia.

• Chemoheterotrophs: Chemical energy source, organic carbon source. Examples: All animals, most fungi, most protists, bacteria.

• Photoautotrophs: Light energy source, CO2 carbon source. Examples: Green plants, cyanobacteria, purple non-sulfur bacteria.

• Photoheterotrophs: Light energy source, organic carbon source. Examples: Green non-sulfur bacteria, purple non-sulfur bacteria.

• Chemoautotrophs: Chemical energy source, CO2 carbon source. Examples: Some prokaryotes (e.g., nitrifying bacteria).

Metabolic Rate

Metabolic rate is the amount of energy needed to keep cells alive and functioning.

• Metabolic Rate: Amount of energy needed to keep cells alive.

• Calorie (cal): Energy required to raise 1 mL of water by 1°C.

• Kilocalorie (kcal): For humans, 1 kcal = 1000 cal.

• Factors affecting metabolic rate:

  • Size of the organism

  • Activity level

  • Temperature

  • Age

• Endotherms: Generate heat from within (mammals and birds).

• Ectotherms: Get heat from the environment (all other animals).

• Kleiber's Law: For endotherms, metabolic rate scales to the 3/4 power of the animal's mass. If you double an animal's mass, its metabolic rate will only increase by about 1.68 times.

• Mass-Specific Metabolic Rate: Metabolic rate per unit body mass is greater for smaller animals than for larger animals.

• Basal Metabolic Rate (BMR): Minimal energy expenditure of an organism at rest.

• Actual Daily Energy Expenditure: BMR plus the energy required for all activity.

Digestion

Digestion is the process by which food is broken down into absorbable components.

• Digestive Process:

  1. Ingestion: Food is taken into the body.

  2. Digestion: Food pieces are dismantled by physically and chemically breaking them into absorbable molecules.

  3. Absorption: Energy-rich food molecules are taken into the cells of the body.

  4. Elimination: Indigestible materials are discarded as waste.

• Human Digestive System:

  • Mouth: Chews and salivates food; salivary amylase digests starch.

  • Stomach: Physically breaks down food with stomach acids.

  • Small Intestine: Enzymes digest all food; secretions of enzyme from pancreas; new bile emulsifies fats; absorption of monomers.

  • Large Intestine: Water, salts, and some vitamins are absorbed; bacteria aid digestion and synthesize vitamins; enzymes eliminate remaining food.

Cellular Respiration

Introduction

Cellular respiration is the process used by all living cells to generate ATP from an energy source (light, organic, or inorganic compounds).

• Aerobic Respiration: In the presence of oxygen; yields the most ATP; all domains.

• Fermentation: In the absence of oxygen; yields less ATP; all domains.

• Anaerobic Respiration: In the absence of oxygen; other molecules accept the electrons (e.g., sulfate, nitrate).

• Redox Reactions: Involve loss or gain of electrons.

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

• Key Equation:

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

• NAD+: Derivative of Vitamin B3 (niacin); removes and carries 2 high-energy electrons.

  • $\mathrm{NAD^+} + 2\mathrm{H} \rightarrow \mathrm{NADH} + \mathrm{H^+}$

• FAD: Derivative of Vitamin B2 (riboflavin); removes and carries 2 high-energy electrons.

  • $\mathrm{FAD} + 2\mathrm{H} \rightarrow \mathrm{FADH_2}$

Stages of Aerobic Respiration

• Glycolysis (Cytoplasm): Splits glucose into two pyruvate molecules (3C each). Net gain of 2 ATP and 2 NADH.

• Krebs Cycle (Mitochondria): Completes breakdown of glucose, produces CO2, ATP, NADH, and FADH2.

• Electron Transport Chain (Mitochondria): Uses NADH and FADH2 to generate ATP and water.

Fermentation

• Occurs in the absence of oxygen.

• Regenerates NAD+ so glycolysis can continue.

• Fermentation in animals: Lactic acid is the product.

• Fermentation in yeast: CO2 and ethanol are the products.

Anaerobic Respiration

• Sulfate or nitrate or other molecules accept the electrons.

• Done in some prokaryotes.

Chromosomes and Cell Division

Introduction

Cell division is essential for growth, repair, and reproduction. Chromosomes carry genetic information and are duplicated and separated during cell division.

• Prokaryotic Cells: Single, circular chromosome attached to the cell membrane.

• Eukaryotic Cells: Free-floating linear chromosomes within a nucleus.

Prokaryotes: Binary Fission

• Prokaryotic cell division.

• DNA is replicated.

• Cell elongates.

• Cell splits.

Eukaryotes: Mitosis

• Eukaryotic cells make new cells with the same genetics.

• Multi-cellular organisms use for growth, maintenance, or to make a new individual.

• Haploid: Single set of chromosomes.

• Diploid: Two sets of chromosomes (one from each parent).

• Polyploid: Sets of 3+ chromosomes.

• Sister Chromatids: Identical copies of a chromosome held together at the centromere.

Stages of Mitosis

1. Interphase: Chromosomes replicate.

2. Prophase: Nuclear membrane breaks down; sister chromatids condense; spindle forms.

3. Metaphase: Sister chromatids line up at the center of the cell.

4. Anaphase: Sister chromatids are pulled apart by the spindle fibers.

5. Telophase: Chromosomes begin to uncoil; the nuclear membrane reassembles; the cell begins to split in two.

6. Cytokinesis: Cytoplasm is divided into the two daughter cells.

Stages of Meiosis

1. Meiosis I: Homologous chromosomes separate.

   • Prophase I: Synapsis and crossing over occur.

   • Metaphase I: Homologous pairs line up at the metaphase plate.

   • Anaphase I: Homologous chromosomes separate.

   • Telophase I and Cytokinesis: Two haploid cells are formed.

2. Meiosis II: Sister chromatids separate.

   • Prophase II: Spindle forms.

   • Metaphase II: Sister chromatids line up at the metaphase plate.

   • Anaphase II: Sister chromatids separate.

   • Telophase II and Cytokinesis: Four haploid daughter cells are formed.

Photosynthesis

Introduction

Photosynthesis is the process by which photoautotrophs make enough food to sustain themselves. It converts light energy into chemical energy stored in glucose.

• Photosynthesis Equation:

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

• Chloroplasts: Organelles where photosynthesis takes place.

Chloroplast Structure

• Double Membrane

• Thylakoid Membrane Sacs

• Thylakoid Space (Lumen)

• Stroma: Location of "synthesis" reactions.

Chlorophyll

• Pigment that absorbs light.

• Located in thylakoids.

Light Reactions ("Photo")

• Occur in the thylakoids.

• Light is captured by chlorophyll.

• Results in high-energy molecules (ATP and NADPH) and oxygen.

• Light energy excites electrons in chlorophyll.

• Energy captured in two photosystems (PSII and PSI).

Synthesis Reactions ("Calvin Cycle")

• Occur in the stroma.

• Light-independent.

• CO2 is fixed into organic molecules (glucose).

Reproduction

Types of Reproduction

• Asexual Reproduction: Offspring arise from a single parent; no fusion of gametes.

  • Binary Fission: Prokaryotes divide into two identical cells.

  • Gemmation/Budding: Offspring grows out of the parent body.

  • Fragmentation: Parent breaks into pieces, and each grows.

• Sexual Reproduction: Two individuals give genetic material to produce offspring. Genetic material is in gametes (egg and sperm).

Human Male Reproductive System

• Testes: Primary male sex organs (gonads); make sperm and testosterone; suspended in the scrotum.

• Testosterone: Major male sex steroid hormone; stimulates spermatogenesis, skeletal muscle growth, and hair growth.

Human Female Reproductive System

• Ovaries: Female gonads; develop oocytes (gametes) and make estrogen and progesterone.

• Estrogen: Major female sex steroid hormone; made by ovarian follicles and corpus luteum.

• Progesterone: Permits and maintains pregnancy; made by the corpus luteum.

Control of Reproduction

• Strategies:

  • Prevent ovulation.

  • Prevent fertilization.

  • Prevent implantation.

Sexually Transmitted Diseases

• Diseases transmitted through sexual contact; can affect reproductive health.