Chloroplasts & Mitochondria Review

Chloroplast Overview

• Site of photosynthesis; contain green pigment (chlorophyll)
• Visible as oval green structures in plant cells
• Work in tandem with mitochondria (respiration) to sustain plant energy balance

Chloroplast Structure

• Bound by a double membrane (outer + inner)
• Internal matrix: stroma (enzyme-rich, DNA, ribosomes)
• Internal membrane system folds into thylakoids
  • Stacks of thylakoids form grana
• Typical length ≈ $5\,\mu\text{m}$; diagram reference indicated $500\,\text{nm}$ scale bar

Functional Adaptations

• Double membrane controls metabolite exchange with cytoplasm
• Thylakoid membranes provide large surface area for embedded photosystems & ATP synthase ➜ efficient light capture & photophosphorylation
• Stroma contains Calvin-cycle enzymes ➜ carbon fixation
• DNA & 70S ribosomes in stroma enable semi-autonomous protein synthesis for rapid response to light conditions

Measurement & Magnification Basics

• Actual size $= \dfrac{\text{image size}}{\text{magnification}}$
• Magnification $= \dfrac{\text{image size}}{\text{actual size}}$
• Use scale bar (e.g., $500\,\text{nm}$) to derive either value; show clear working in exam answers

Chloroplast vs. Mitochondrion – Key Comparison

Exam Tips

• Always label: outer membrane, inner membrane, stroma, thylakoid, granum, starch grain, lipid droplet (if present)
• In calculations: keep units consistent (e.g., convert $\mu\text{m}$ to $\text{nm}$ when needed)
• Table answers: use ruled columns, clear headings, parallel grammar