BIO I STUDY GUIDE

Below is a clean, fresh explanation of photosynthesis and cellular respiration—detailed, clear, and easy to study, with a memory trick at the end.

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PHOTOSYNTHESIS

Purpose:

Plants (and some bacteria/algae) use sunlight to make glucose (chemical energy) from CO₂ + H₂O, releasing O₂.

Overall Equation:

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

Photosynthesis happens in the chloroplast.

1. Light-Dependent Reactions (Thylakoid Membranes)

Uses sunlight + water → makes ATP, NADPH, and O₂

Steps:

  • Sunlight hits PSII, energizes electrons.

  • Water is split (photolysis) → releases O₂, H+, and e-.

  • Electrons move down ETC → make ATP.

  • At PSI, electrons re-energize → make NADPH.

Products: ATP + NADPH + O₂

2. Light-Independent Reactions (Calvin Cycle) — Stroma

Uses ATP + NADPH to turn CO₂ → glucose.

Phases:

  1. Carbon fixation – CO₂ + RuBP using enzyme Rubisco

  2. Reduction – makes G3P (a sugar molecule)

  3. Regeneration – RuBP is rebuilt

Product: G3P → used to build glucose

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CELLULAR RESPIRATION

Purpose:

Cells break down glucose to make ATP.

Occurs in mitochondria.

Overall Equation:

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

1. Glycolysis (Cytoplasm)

Glucose → 2 Pyruvate + 2 ATP + 2 NADH

No oxygen required.

2. Pyruvate Oxidation (Mitochondrial Matrix)

Each pyruvate → Acetyl-CoA + CO₂ + NADH

3. Krebs Cycle / Citric Acid Cycle (Matrix)

Acetyl-CoA is broken down.

Products (per glucose):

  • 6 NADH

  • 2 FADH₂

  • 2 ATP

  • 4 CO₂

4. ETC + Chemiosmosis (Inner Mitochondrial Membrane)

Most ATP is made here.

Steps:

  • NADH & FADH₂ give electrons to ETC.

  • H⁺ ions pumped across membrane.

  • Oxygen is the final electron acceptor → forms water.

  • H⁺ flows through ATP synthase → lots of ATP.

Total ATP: ~30–34 ATP

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How the Two Processes Connect

  • Photosynthesis makes glucose + O₂ that respiration uses.

  • Cellular respiration makes CO₂ + H₂O that photosynthesis uses.

It’s a biological cycle.

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MEMORY TRICK

“Photosynthesis Puts in energy; Respiration Releases it”

  • P = Put in sunlight

  • R = Release ATP

For steps:

Photosynthesis: “Light First, Sugar Second”

  • Light-dependent → ATP & NADPH

  • Light-independent → Glucose

Respiration: “Go Pick Killer Energy”

  • G = Glycolysis

  • P = Pyruvate oxidation

  • K = Krebs cycle

  • E = ETC

Here are clear, detailed explanations of the organelles you asked for AND a simple memory trick, plus an explanation of the cytoskeleton’s structure.

📦 Golgi Apparatus

What it is:

A stack of flattened membrane sacs (looks like pancakes).

What it does:

  • Modifies proteins + lipids

  • Sorts them

  • Packages them into vesicles

  • Sends them where they need to go (inside or outside the cell)

Think of it as:

The post office of the cell.

🌫 SER — Smooth Endoplasmic Reticulum

Structure:

Smooth, tube-like membranes with no ribosomes.

Functions:

  • Makes lipids (fats, steroids)

  • Detoxifies drugs/alcohol

  • Stores calcium in muscle cells

Think of it as:

The lipid factory + detox center.

🧵 RER — Rough Endoplasmic Reticulum

Structure:

Flattened sacs covered in ribosomes → looks rough.

Functions:

  • Makes proteins (the ribosomes do the building)

  • Modifies proteins inside its lumen

  • Sends proteins to the Golgi

Think of it as:

The protein factory.

🧪 Lysosomes

Structure:

Membrane-bound sacs filled with digestive enzymes.

Functions:

  • Break down old cell parts

  • Digest food particles

  • Destroy bacteria the cell absorbs

  • Do apoptosis (programmed cell death)

Think of it as:

The recycling center or garbage disposal.

🔥 Peroxisomes

Structure:

Small membrane-bound organelles containing oxidizing enzymes.

Functions:

  • Break down fatty acids

  • Detoxify harmful substances (especially H₂O₂—hydrogen peroxide)

  • Produce catalase to break down peroxide safely

Think of it as:

The hazmat detox team.

🧠 MEMORY TRICK for These Organelles

Use the phrase:

“Good Students Read Lots of Pages.”

Each first letter stands for an organelle:

  • Good → Golgi (packages)

  • Students → SER (lipids + detox)

  • Read → RER (proteins)

  • Lots → Lysosomes (digest)

  • Pages → Peroxisomes (detox peroxide)

🕸 Cytoskeleton Structures (Detailed)

The cytoskeleton is a network of fibers that gives the cell structure, allows movement, and organizes organelles. It has three main components:

1⃣ Microfilaments (Actin Filaments)

Structure:

  • Thin, solid rods made of actin protein

  • Smallest cytoskeleton fiber

Functions:

  • Cell movement (muscle contraction)

  • Cell shape changes

  • Cytokinesis (splitting cell during division)

  • Helps with cell crawling (like amoebas)

2⃣ Intermediate Filaments

Structure:

  • Rope-like fibers made of keratins or similar proteins

  • Medium size

  • Very strong and stable

Functions:

  • Maintain cell shape

  • Anchor organelles (like the nucleus)

  • Resist tension (keeps cell from tearing)

3⃣ Microtubules

Structure:

  • Hollow tubes made of tubulin

  • Largest cytoskeleton fiber

Functions:

  • Form mitotic spindle (pull chromosomes apart)

  • Form cilia & flagella

  • Track “roads” for vesicle transport (with motor proteins)

  • Maintain cell shape

🧠 MEMORY TRICK for Cytoskeleton

Use this phrase:

“MicroFILaments FLEX, Intermediate Filaments INSURE, MicroTUBules TRANSPORT.”

  • MF = FLEX → movement, muscle action

  • IF = INSURE → protect, stabilize

  • MT = TRANSPORT → vesicle highways + cell division

Or shorter:

“Small flex, medium protect, big transport.”

If you want, I can also make a matching diagram, quiz, flashcards, or a comparison table.

If you want, I can make a side-by-side comparison chart, test questions, or flashcards!