adult human

tallest trees

chicken egg

frog embryo

most eukaryotic cells

mitochondrionmost bacteria

virus

proteins

atoms

diameter of DNAdouble helix

Quick Review:

• Where does most of the cell's work take place?

• What happen to the proteins once they leave the golgi apparatus and enter the cytoplasm?

Cytoplasm

• become plasma membrane protein,

• stay in the cytoplasm for use in the cell,

• stored in vesicles until needed for transport.

What is a Cell?

• Cell: basic or smallest living unit of life of a living organism.

• Protoplasm: complex jelly-like substance.

• 70% is water; rest is mineral salts, proteins, carbohydrates, fats.

• Made up of 3 main parts: (i) Cytoplasm(ii)Cell surface membrane(iii)Nucleus

• Part of the protoplasm between cell membrane & nucleus

• Jelly-like fluid in which many chemical reactions or cell activities take place.

• 90% water; enzymes, organelles (specialized structures)

(i) Cytoplasm

flagellum

cytoplasmrough endoplasmicreticulum

ribosome

mitochondrion

Golgi complex

plasmamembrane

vesicle

smooth endoplasmicreticulum

free ribosomevesicle

nuclear porechromatin (DNA)

nucleolusnuclear envelope

nucleus

• Partially-permeable membrane• Controls movement of substances

into and out of the cell.• Allows only some substances to cross

it. (e.g. small molecules: glucose, water,

O2, CO2

- prevents larger molecules from crossing: starch, proteins

(ii) Cell surface membrane

An electron micrograph of a cell membrane (of a human red blood cell) seen in cross-section.

• made of proteins and fats• double phospholipid layers(fats, proteins, phosphate groups)

• Parts of a nucleus: - Nuclear envelope, nucleoplasm, nucleolus

• Nucleoplasm: dense material inside nucleus

• Nucleolus(1) or nucleoli (2): Making proteins.’

• Control cell activities e.g. cell growth, repair of worn-out parts.• Essential for cell division.

(iii) Nucleus

nuclear pores

chromatin

nucleolus

nuclear envelope

• Chromatin: Network of long, thread-like structures

• Contains hereditary material (DNA and proteins), instructions for the cell to carry out all chemical reactions

• Controls cell division• Chromosomes: when chromatin threads

condense and become highly coiled during cell division (rod-shaped)

• Non-living layer • Made up of Cellulose (a complex sugar)• Surrounds cell membrane of plant cell• Fully permeable to water, gases, dissolved

substances- Protects the plant cell from injury- Supports and gives a fixed shape to plant cell

Plant cells – Cell Wall

Membrane Network – Endoplasmic Reticulum (ER)

0.5 micrometers

smooth endoplasmic reticulum

vesicles

ribosomes

rough endoplasmic reticulum

0.5 micrometers

• 2 types: rough and smooth• For synthesis and transport of

substances• Rough ER (RER): ribosomes are attached

on outer surface• Continuous with nuclear envelope• Transports proteins made by ribosomes

to Golgi Apparatus for secretion out of the cell.

Endoplasmic reticulum

• Smooth ER (SER): no ribosomes attached on outer surface

• Makes substances – fats, steroids (sex hormones in mammals)

• Detoxification – converts harmful substances into harmless materials.

Endoplasmic reticulum

• Small round structures• Needed to make proteins in the

cell• 1. Attached to RER membrane –

make proteins that are transported out of the cell

• 2. Free ribosomes in the cytoplasm – make proteins that are used within cytoplasm of the cell

Ribosomes

• Stack of flattened spaces surrounded by membranes

• Vesicles: tiny round structures enclosed by a membrane

• Fuse on one side and pinch off from opposite side of Golgi apparatus

• Stores and modifies substances made by ER

• Packages the substances in vesicles for secretion out of the cell

Golgi Apparatus

ORGANELLESMITOCHONDRION (mitochondria):

• “Power house” of a cell• Aerobic respiration: food substances are

oxidized to release energy• Energy is used for cell activities e.g.

growth, reproduction, movement etc.

• Oval shaped structures• Contain green pigment chlorophyll• Absorbs sunlight for photosynthesis, for

plants to make food

PLANT CELLS - Chloroplasts

VACUOLES• Fluid-filled space enclosed by membrane• Storage of various substances • Animal cells: many small vacuoles; store

water, food. Exist temporarily• Plant cells: one large, central vacuole,

filled with cell sap, contains dissolved substances e.g. sugars, mineral salts, amino acids, helps to maintain shape of plant cell

• Membrane – tonoplast

ORGANELLES

chloroplast

central vacuole

rough endoplasmicreticulum

ribosomes

cell wall

mitochondrion

Golgi complex

plasmamembrane

smooth endoplasmicreticulum

free ribosome

vesicle

nuclear porechromatin

nucleolus

nuclear envelope

nucleus

CENTRIOLES• Small, hollow cylinders.• Found as a pair near the nucleus.• Play an important part in cell division.• Only in animal cells. Absent in plant

cells.

ORGANELLES

Differences between plant and animal cells

Feature Plant cell Animal cell Cell wall Cell wall present Cell wall absent

No. and size of vacuoles

1 large permanent vacuole

Numerous small vacuoles

Relative size Large Small

Chloroplast Chloroplasts present Absent

Shape Regular, elongated, cylindrical

Irregular

Centrioles Centrioles absent Centrioles present

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