Chapter 4Section 2 Cell Structure and

Function

ReviewWho am I? What did I do?

Robert Hooke

Robert Hooke• He was an English scientist who cut a thin slice of

cork and looked at it with a homemade microscope in 1665.

• Hooke compared what he observed to the cells, or box-like rooms, in which monks slept.

• Therefore he named the structures that make up cork “cells.”

Review: Who am I?

Anton van LeeuwenhoekAnton van Leeuwenhoek

was a Dutch was a Dutch lens makerlens maker, who , who was the first person to observe was the first person to observe living cellsliving cells..

Anton van Leeuwenhoek• used a simple microscope he had made to

observe such things as blood, rainwater, and teeth scrapings.

• In 1675, he observed single-celled organisms in a drop of pond water, which he called these tiny living things “animalcules.”

Review: Cell Theory

• Key players in the Cell Theory:– Matthias Schleiden

– Theodor Schwann

– Rudolph Virchow

Cell structure and Function• In the cell theory, cells are described as the

basic unit of structure and function in living things.

• Do you know why the cell is described this way?– Example: brick house

Cell structure and Function (cont.)• Many different kind of cells make up your body.• In fact, every cell in your body is adapted to its

function.• Most cells are very small.• Plant and animal cells usually are between 10 and

50 micrometers in size.• The smallest cell may be 0.2 micrometers in

diameter.

Cell structure and Function (cont.)• Some cells may be very large.• Several nerve-cell axons in your legs are about 1

meter long.• A large cell that is found in many animals is an

egg.– Ex: a single cell that you probably see everyday is a

chicken egg.

• How many cells do you think make up and ostrich egg?

Main Cell Parts• What are the 3 main cell structures that control

most of the activities in the cell?– Cell membrane– Nucleus– Cytoplasm

Cell Membrane• Cells are enclosed by a thin structure called the

cell membrane.– It is a living part of the cell made mostly of lipids and

proteins.– It is sometimes called the plasma membrane.

Cell Membrane (cont.)• The cell membrane has 3 important jobs:– Protect the inside of the cell by separating the cell

from its surroundings.– Support the cell and give it shape.– Controls the passage of substances into and out of

the cell.

Cell Wall• Some cells, such as plant cells, have a structure

surrounding the cell membrane called the cell wall.– Unlike the cell membrane, the cell wall is not a living

part of the cell.

• Cell wall is made mostly of cellulose.– It is a carbohydrate made up of many sugar molecules

linked together. – The cell wall also contains pectin, which is a starch

used to thicken jams and jellies.

Cell Wall (cont.)• The cell wall has several functions:– It protects the cell and give it shape.– Provides cell with support.– Because of the support provided by the cell wall,

large plants do not need a skeleton.

Nucleus• The nucleus is the “control center” of the cell.– It controls most of the activities that take place in the

cell.– It controls cell reproduction.

• What would happen to a cell if the nucleus were removed?– The cell would not be able to carry on its activities or

reproduce. It would die.

Nucleus (cont.)• The nucleus is separated from the rest of the cell

by the nuclear membrane.• Like the cell membrane, the nuclear membrane

has 3 jobs. What do you think the 3 jobs are?– Protects the inside of the nucleus.– Support the nucleus and give it shape.– Controls the passage of substances into and out of

the nucleus.

Nucleus (cont.)• Within the nucleus there are nucleoli, which

makes rRNA.– These molecules are involved in making

proteins.

• Chromosomes are also located in the nucleus.– They control heredity.• Heredity is the passing of traits from parent to

offspring.

Cytoplasm• Cytoplasm is all the living substance in a cell

except the nucleus.• Most of the life processes take place within the

cytoplasm of the cell.