Photosynthesis and Cellular Reproduction: Study Guide (Chapters 7 & 8)

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Photosynthesis: Using Light to Make Food

7.1 Photosynthesis Powers Most Life on Earth

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, sustaining most life on Earth. Understanding the types of organisms involved is essential.

Chemotrophs: Organisms that obtain energy by oxidizing inorganic or organic chemicals rather than from light.
Autotrophs: Organisms that produce their own food from inorganic substances. They are the primary producers in ecosystems.
Photoautotrophs: Autotrophs that use light energy to synthesize organic compounds from carbon dioxide. Examples include plants, algae, and cyanobacteria.
Heterotrophs: Organisms that cannot synthesize their own food and must obtain organic molecules by consuming other organisms.

Example: Green plants are photoautotrophs, while animals and fungi are heterotrophs.

7.2 Photosynthesis Occurs in Chloroplasts in Plant Cells

Photosynthesis takes place in specialized organelles called chloroplasts, primarily within the mesophyll cells of leaves.

Chloroplasts: Double-membraned organelles in plant cells where photosynthesis occurs.
Stroma: The thick fluid inside the chloroplast where the Calvin cycle (sugar synthesis) takes place.
Mesophyll: Leaf cells specialized for photosynthesis; chloroplasts are concentrated here.
Thylakoids: Membranous sacs within chloroplasts containing chlorophyll; arranged in stacks called grana (singular: granum).
Stomata: Tiny pores on the leaf surface through which CO2 enters and O2 exits.

Example: In a typical plant cell, the chloroplast contains an outer membrane, inner membrane, stroma, thylakoid membranes, and grana.

7.4 Photosynthesis is a Redox Process

Photosynthesis involves redox reactions, where electrons are transferred between molecules.

Redox Reaction: A chemical reaction involving the transfer of electrons from one substance to another. "Redox" stands for reduction-oxidation.
In photosynthesis, water is oxidized (loses electrons) and carbon dioxide is reduced (gains electrons).

Equation:

7.5 Photosynthesis Occurs in Two Stages, Linked by ATP and NADPH

Photosynthesis consists of two main stages: the light reactions and the Calvin cycle. These stages are connected by energy carriers ATP and NADPH.

Light Reactions: Occur in the thylakoid membranes; convert solar energy to chemical energy, producing ATP, NADPH, and O2.
Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to synthesize sugars from CO2.
Products of Light Reactions: ATP, NADPH, O2

7.6 Visible Radiation Absorbed by Pigments Drives the Light Reactions

Light energy is absorbed by pigments, initiating the light reactions of photosynthesis.

Electromagnetic Spectrum: The range of all types of electromagnetic radiation, including visible light, which is used in photosynthesis.

Example: Chlorophyll absorbs light primarily in the blue and red wavelengths.

7.7 Photosystems Capture Solar Energy

Photosystems are complexes in the thylakoid membrane that capture and convert solar energy.

Photosystem: A cluster of pigments and proteins that absorb light energy and transfer electrons.
The reaction center contains a special pair of chlorophyll a molecules.

7.9 The Light Reactions Take Place Within the Thylakoid Membranes

The light reactions occur in the thylakoid membranes, where ATP is synthesized and electrons are transferred.

ATP Synthase: An enzyme complex that synthesizes ATP from ADP and inorganic phosphate, powered by a flow of protons across the thylakoid membrane.
Electrons lost from the reaction center of photosystem II are replaced by electrons from water (H2O), releasing O2 as a byproduct.

Equation for ATP Synthesis:

The Cellular Basis of Reproduction and Inheritance

8.1 Cell Division

Cell division is the process by which cells reproduce, essential for growth, repair, and reproduction in living organisms.

Asexual Reproduction: A single parent produces genetically identical offspring; only one individual is required. Example: binary fission in bacteria.
Sexual Reproduction: Two parents contribute genetic material to produce genetically unique offspring. Example: fertilization in animals and plants.
Except for identical twins, siblings from the same parents are similar but not identical due to genetic recombination.

8.3 Eukaryotic vs. Prokaryotic Cells

Eukaryotic and prokaryotic cells differ in structure and complexity.

Eukaryotic Cells: Larger, more complex, contain many genes, and have a membrane-enclosed nucleus.
Prokaryotic Cells: Smaller, simpler, lack a nucleus.
Sister Chromatids: Identical copies of a chromosome joined together at a region called the centromere.

8.4 The Cell Cycle and Interphase

Eukaryotic cells spend most of their life in interphase, a period of growth and DNA replication.

Interphase: The phase in which the cell grows, performs its normal functions, and duplicates its DNA in preparation for cell division.
Most of a cell's life is spent in interphase.

8.5 Mitosis: Key Stages

Mitosis is the process of nuclear division in eukaryotic cells, consisting of several stages.

Prophase: The mitotic spindle begins to form.
Metaphase: Chromosomes align at the cell's equator; spindle fibers attach to centromeres.
Telophase: The nuclear envelope re-forms around the separated chromosomes.

8.6 Plant vs. Animal Cell Division

Plant and animal cells divide by different mechanisms due to structural differences.

Plant Cells: Form a cell plate during cytokinesis, which develops into a new cell wall.
Animal Cells: Divide by cleavage, forming a cleavage furrow.
Plant cells have rigid cell walls; animal cells do not.

8.7 Regulation of Cell Division

Cell division is regulated by various factors, including physical contact with other cells.

Density-Dependent Inhibition: The phenomenon where crowded cells stop dividing; a physical factor that regulates growth rate in animal cells.
Main Factor: Likely due to the lack of available space and growth factors when cells are crowded.

8.11 Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes that carry genes for the same traits.

Homologous Chromosomes: Two chromosomes in a nucleus that carry genes controlling the same inherited characteristics.

8.18 Nondisjunction

Nondisjunction is an error in cell division that can lead to genetic disorders.

Nondisjunction: An accident during meiosis or mitosis when members of a chromosome pair (sister chromatids or homologous chromosomes) fail to separate properly at anaphase.
This can result in gametes or cells with abnormal numbers of chromosomes.

Example: Down syndrome is caused by nondisjunction resulting in an extra copy of chromosome 21.