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 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

Equation for Photosynthesis:

$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Equation for Cellular Respiration:

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

Organisms That Undergo Photosynthesis

• Plants (e.g., Arabidopsis thaliana)

• Algae (e.g., Chlamydomonas)

• Cyanobacteria

Structure and Function of Plant/Cell Parts

• Chloroplast: Site of photosynthesis; contains thylakoids and stroma.

• Thylakoid: Membranous sacs where light reactions occur.

• 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 (e.g., animals, fungi).

Stages of Photosynthesis: Light Reactions and Calvin Cycle

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

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

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

Flow of Electrons in Photosynthesis

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

• Oxygen is produced as a byproduct from the splitting of water.

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; absorbs blue-violet and red light.

• Chlorophyll b: Accessory pigment; broadens absorption spectrum.

• Carotenoids: Accessory pigments; 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

Type	CO2 Fixation	Adaptation
C3	Directly via Calvin cycle	Most plants; less efficient in hot, dry climates
C4	CO2 fixed into 4-carbon compound	Adapted to high light, temperature; minimizes photorespiration
CAM	CO2 fixed at night	Adapted to arid conditions; stomata open at night

The Cell Cycle

Phases of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It consists of interphase and the mitotic (M) phase.

• Interphase: Includes G1 (cell growth), S (DNA synthesis), and G2 (preparation for mitosis).

• M Phase: Includes mitosis (nuclear division) and cytokinesis (cytoplasm division).

Phase	Main Events
G1	Cell growth, organelle duplication
S	DNA replication
G2	Preparation for mitosis
Mitosis	Division of nucleus
Cytokinesis	Division of cytoplasm

Key Structures: Centrioles, Centrosomes, Centromeres, Kinetochores

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

• Centrosome: Microtubule-organizing center; contains centrioles in animal cells.

• Centromere: Region where sister chromatids are joined.

• Kinetochore: Protein complex on centromere; attaches chromosomes to spindle fibers.

Mitotic Spindle

• Structure made of microtubules; essential for chromosome movement 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; spindle forms.

• Metaphase: Chromosomes align at metaphase plate.

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

• Telophase: Nuclear envelopes reform; chromosomes decondense.

Meiosis and Sexual Reproduction

Function of Meiosis vs. Mitosis

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

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

Phases of Meiosis Compared to Mitosis

• Meiosis involves two divisions (Meiosis I and II), resulting in four non-identical haploid cells.

• Mitosis involves one division, resulting in two identical diploid cells.

Key Terms

• Gametes: Haploid reproductive cells (sperm, egg).

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

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

• Synapsis: Pairing of homologous chromosomes during prophase I.

• Crossing Over: Exchange of genetic material between homologous chromosomes.

• 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).

• 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: Structure formed after gastrulation with three germ layers.

Determination vs. Differentiation

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

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

Sequence of Development

1. Fertilization

2. Cleavage (formation of blastula and blastocoel)

3. Gastrulation (formation of gastrula and germ layers)

4. Neurulation (formation of neural tube)

5. Organogenesis (formation of organs)

Additional info: The timing and details of each phase can vary among animal species, but the general sequence is conserved.