Cell Structure and Function

The cell is the basic unit of life, and organelles such as the nucleus, mitochondria, ER, and Golgi share the work. The nucleus manages genetic information, mitochondria make ATP, and ribosomes synthesize proteins. Plant cells have a cell wall, chloroplasts, and a large vacuole, and secreted proteins travel from the ER through the Golgi to the membrane. Use the slider to pick each organelle and explore its place and role.

Cell = the basic unit of life

🔬 A cell is like a city

①Nucleus = city hall (manages genetic info, sends commands)

②Mitochondria = power plant (produces ATP energy)

③ER = factory (synthesizes proteins/lipids), Golgi = logistics center (packaging/delivery)

Explore Organelles

Select organelle0

💡 Inspect each organelle

①0=Nucleus: DNA storage, transcription control, nuclear envelope (double)

②1=Mitochondria: cellular respiration (ATP), own DNA

③2=ER: rough (ribosomes, proteins), smooth (lipid synthesis)

④6=View all: see all organelles together!

Organelle Reference

Organelles

ListFunctions of key organelles

Nucleus

double membrane, DNA, nucleolus (rRNA)

genetic info storage/expression

Mitochondria

double membrane, own DNA, cristae

ATP production (respiration)

Rough ER

ribosomes attached, secretory proteins

protein synthesis/transport

Smooth ER

no ribosomes, abundant in liver cells

lipid synthesis, detox

Golgi

flattened sacs (cisternae)

modify and secrete

Ribosome

RNA + protein, no membrane

protein synthesis

Lysosome

contains hydrolytic enzymes

intracellular digestion

Animal Cell vs Plant Cell

Cell comparison

ChartAnimal vs Plant cell

Item	Animal	Plant
Cell wall	absent	present (cellulose)
Chloroplast	absent	present (photosynthesis)
Centrosome	present	absent (mostly)
Vacuole	small (multiple)	large (single)
Lysosome	present	absent (vacuole substitutes)

Worked Examples and Exam Practice

Example 1

A protein secreted out of the cell, like a digestive enzyme from the pancreas, is synthesized and transported. List its route in order.

The secretory protein is synthesized on ribosomes attached to the rough ER (rER).

Entering the rER, the protein is loaded into transport vesicles and moves to the Golgi.

After processing in the Golgi, a secretory vesicle fuses with the cell membrane and releases the protein.

▸ ribosome (rER) → ER → Golgi → secretory vesicle → cell membrane

Membrane-bound organelles form an assembly line that produces, processes, and ships proteins. The ribosome itself has no membrane.

Example 2

A cell shows a cell wall, chloroplasts, and one large central vacuole, but no centrosome or lysosome. Is it an animal or a plant cell?

A cell wall (cellulose) and chloroplasts are found only in plant cells.

A single large vacuole is also typical of plant cells, which usually lack a centrosome and lysosomes.

▸ Plant cell

Nucleus, mitochondria, ribosomes, ER, and Golgi are shared; a cell wall, chloroplasts, and a large vacuole mark a plant cell.

CSAT-style

Which statement about animal-cell organelles is correct?

①The ribosome is enclosed by a single membrane

②Mitochondria have no DNA of their own

③The ribosome has no membrane and carries out protein synthesis (translation)

④The Golgi apparatus carries out photosynthesis

⑤The lysosome produces ATP

▸ ③ The ribosome has no membrane and carries out protein synthesis (translation)

A ribosome is a membrane-less particle of rRNA and protein that translates mRNA into protein.

Mitochondria do have their own DNA (②), chloroplasts do photosynthesis (④), and mitochondria make ATP (⑤), so the others are wrong.

Summary

Cell function summary

nucleus(gene) → ribosome(synthesis) → ER(transport) → Golgi(secretion) → membrane

secretory pathway = central dogma product exits the cell

🎯 Exam Points

①Nucleus: double membrane, DNA, gene expression control

②Mitochondria: double membrane, own DNA, ATP production

③Ribosome: no membrane, protein synthesis (translation)

④Secretory path: rER → Golgi → membrane

⑤Plant-only: cell wall, chloroplast, large vacuole

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Biology I · Ecosystems

Cellular Respiration

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