Photosynthesis, The Cell Cycle, Meiosis, and Animal Development: Study Guide

Ch. 10: Photosynthesis

Overview and Comparison with Cellular Respiration

Photosynthesis is the process by which autotrophic organisms convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. Cellular respiration, in contrast, is the process by which cells break down glucose to produce ATP, releasing carbon dioxide and water as byproducts.

• Photosynthesis: Occurs in chloroplasts, uses light energy, produces glucose and O2.

• Cellular Respiration: Occurs in mitochondria, uses glucose and O2, produces ATP, CO2, and H2O.

• 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, algae, and some prokaryotes (e.g., cyanobacteria) are capable of photosynthesis.

• These organisms are called autotrophs because they produce their own food.

Structure and Function of Plant/Cell Parts

• Chloroplasts: Organelles where photosynthesis occurs; contain thylakoids (site of light reactions) and stroma (site of Calvin cycle).

• Thylakoid membrane: Contains chlorophyll and other pigments; location of the electron transport chain.

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

Autotrophs vs. Heterotrophs

• Autotrophs: Organisms that produce organic molecules from inorganic sources (e.g., plants).

• Heterotrophs: Organisms that obtain organic molecules by consuming other organisms (e.g., animals, fungi).

Stages of Light Reactions and Calvin Cycle

• 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.

• Reactants and Products:

  • Light Reactions: Reactants – H2O, light; Products – O2, ATP, NADPH

  • Calvin Cycle: Reactants – CO2, ATP, NADPH; Products – Glucose, ADP, NADP+

Flow of Electrons in Photosynthesis

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

• This flow is essential for the reduction of CO2 in the Calvin cycle.

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; absorbs blue-violet and red light.

• Chlorophyll b: Accessory pigment; broadens the spectrum of absorbed light.

• Carotenoids: Accessory pigments; protect chlorophyll from 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 Plant Processes

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

• C4 Plants: Minimize photorespiration by separating carbon fixation and the Calvin cycle in space (mesophyll and bundle-sheath cells).

• CAM Plants: Minimize water loss by opening stomata at night; separate carbon fixation and the Calvin cycle in time.

Ch. 12: The Cell Cycle

Phases of the Cell Cycle

The cell cycle consists of interphase (G1, S, G2) and the M phase (mitosis and cytokinesis). Each phase has distinct events that prepare the cell for division.

• G1 Phase: Cell growth and normal functions.

• S Phase: DNA replication.

• G2 Phase: Preparation for mitosis; synthesis of microtubules.

• M Phase: Mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Centrioles, Centrosomes, Centromeres, and Kinetochores

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

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

• Centromeres: Region where sister chromatids are joined; site of kinetochore formation.

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

Mitotic Spindle

• Structure made of microtubules that segregates chromosomes during mitosis.

• Originates from centrosomes and attaches to kinetochores.

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 the metaphase plate.

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

• Telophase: Nuclear envelopes reform, chromosomes decondense.

Ch. 13: Meiosis and Sexual Reproduction

Function and Comparison with Mitosis

• Meiosis: Reduces chromosome number by half, producing four genetically unique gametes.

• Mitosis: Produces two genetically identical daughter cells for growth and repair.

Phases of Meiosis

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

Key Terms

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

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

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

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

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

Ch. 47: 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.

Details of Developmental Stages

• Blastula: Hollow ball of cells; contains the blastocoel (fluid-filled cavity).

• Gastrula: Structure with three germ layers formed during gastrulation.

• Neurulation: Formation of the neural tube from ectoderm.

Determination vs. Differentiation

• Determination: Process by which cells become committed to a specific fate.

• Differentiation: Process by which cells acquire specialized functions and structures.

Sequence of Development

• Fertilization → Cleavage → Blastula → Gastrulation → Neurulation → Organogenesis