Exam 3 Study Guide: Photosynthesis, Cell Cycle, Meiosis, and Animal Development

Photosynthesis

Overview and Comparison with Cellular Respiration

Photosynthesis and cellular respiration are essential biological processes that manage energy flow in living organisms. Both involve electron transport chains and redox reactions, but their overall purposes and products differ.

• Photosynthesis: Converts light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

• Cellular Respiration: Breaks down glucose to release energy, producing carbon dioxide and water as byproducts.

Process	Reactants	Products	Location
Photosynthesis	CO2, H2O, Light	Glucose, O2	Chloroplasts
Cellular Respiration	Glucose, O2	CO2, H2O, ATP	Mitochondria

Organisms That Undergo Photosynthesis

• Plants

• Algae

• Certain bacteria (e.g., cyanobacteria)

Structure and Function of Plant/Cell Parts

• Chloroplast: Organelle where photosynthesis occurs; contains thylakoids and stroma.

• Thylakoid: Membranous sacs containing chlorophyll; site of light reactions.

• Stroma: Fluid surrounding thylakoids; site of the Calvin cycle.

Autotrophs vs. Heterotrophs

• Autotrophs: Organisms that produce their own food from inorganic substances (e.g., plants).

• Heterotrophs: Organisms that obtain energy by consuming other organisms.

Stages of Photosynthesis

• Light Reactions: Occur in the thylakoid membranes; convert light energy to chemical energy (ATP and NADPH); split water to release O2.

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to convert CO2 into glucose.

Stage	Location	Reactants	Products
Light Reactions	Thylakoid membrane	H2O, Light, NADP+, ADP	O2, NADPH, ATP
Calvin Cycle	Stroma	CO2, NADPH, ATP	Glucose, NADP+, ADP

Flow of Electrons in Photosynthesis

• Electrons flow from water to NADP+ via photosystems II and I, generating ATP and NADPH.

Oxidation/Reduction in Photosynthesis

• Oxidation: Loss of electrons (e.g., water is oxidized to O2).

• Reduction: Gain of electrons (e.g., NADP+ is reduced to NADPH).

Pigments of Plants

• Chlorophyll a: Main pigment in photosynthesis.

• Chlorophyll b: Accessory pigment.

• Carotenoids: Accessory pigments that protect against photo-damage.

Linear Electron Flow vs. Cyclic Electron Flow

• Linear Electron Flow: Involves both photosystems; produces ATP and NADPH; releases O2.

• Cyclic Electron Flow: Involves only photosystem I; produces ATP but not NADPH or O2.

C3, C4, and CAM Plants

• C3 Plants: Use the Calvin cycle directly; most common; less efficient under hot, dry conditions.

• C4 Plants: Minimize photorespiration by separating initial CO2 fixation and the Calvin cycle in different cell types.

• CAM Plants: Open stomata at night to fix CO2; Calvin cycle occurs during the day.

The Cell Cycle

Phases of the Cell Cycle

• Interphase: Period of cell growth and DNA replication; includes G1, S, and G2 phases.

• M Phase (Mitotic Phase): Includes mitosis and cytokinesis; the cell divides into two daughter cells.

Phase	Main Events
G1	Cell growth, organelle duplication
S	DNA replication
G2	Preparation for mitosis
M	Mitosis and cytokinesis

Key Structures

• Centrioles: Cylindrical structures involved in spindle formation (animal cells).

• Centrosomes: Microtubule-organizing centers; contain centrioles in animal cells.

• Centromeres: The region where sister chromatids are joined.

• Kinetochores: Protein complexes on centromeres where spindle fibers attach.

Mitotic Spindle

• Structure made of microtubules that segregates chromosomes during mitosis.

Density-Dependent Inhibition and Anchorage Dependence

• Density-dependent inhibition: Cells stop dividing when crowded.

• Anchorage dependence: Cells must be attached to a substrate to divide.

Stages of Mitosis

• Prophase: Chromosomes condense, and the spindle forms.

• Metaphase: Chromosomes align at the metaphase plate.

• Anaphase: Sister chromatids separate and move to opposite poles.

• Telophase: Nuclear envelopes reform, chromosomes decondense.

Meiosis and Sexual Reproduction

Function and Comparison with Mitosis

• Meiosis: Produces gametes (sperm and eggs) with half the chromosome number; introduces genetic variation.

• Mitosis: Produces identical somatic cells for growth and repair.

Phases of Meiosis

• Two divisions: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate).

Key Terms

• Gametes: Haploid reproductive cells (n).

• Homologous Chromosomes: Chromosome pairs with genes for the same traits.

• Independent Assortment: Random distribution of homologous chromosomes during meiosis I.

• Synapsis/Crossing Over: Homologous chromosomes pair and exchange genetic material during prophase I.

• Random Fertilization: Any sperm can fertilize any egg, increasing genetic diversity.

Animal Development

Phases of Embryonic Development

• Fertilization: Fusion of sperm and egg to form a zygote.

• Cleavage: Rapid cell divisions without growth, forming a blastula.

• Gastrulation: Formation of germ layers (ectoderm, mesoderm, endoderm) and the gastrula.

• Neurulation: Formation of the neural tube, precursor to the nervous system.

Key Structures and Terms

• Blastula: Hollow ball of cells formed after cleavage.

• Blastocoel: Fluid-filled cavity inside the blastula.

• Gastrula: A structure with multiple germ layers formed during gastrulation.

Determination vs. Differentiation

• Determination: Process by which a cell becomes committed to a specific fate.

• Differentiation: The process by which a cell develops into its final form and function.

Sequence of Development

1. Fertilization

2. Cleavage

3. Blastula formation

4. Gastrulation

5. Neurulation

6. Organogenesis (formation of organs)

Additional info: The above sequence and definitions are standard in animal developmental biology and provide a framework for understanding embryogenesis in vertebrates.