Biology chapter 1
What is a Cell?
• Cells are the basic building blocks of all living organisms,
from microscopic bacteria to large animals
• They are the smallest structural and functional units
capable of independent existence
• All body organs and plant parts are composed of cells
• Cells have their own life cycle - they die and are replaced by
new cells
Historical Developmentf of gi c
• Antony van Leeuwenhoek (1632-1723): Built the first
microscope using simple lenses, achieving 200x magnification
• Robert Hooke (1635-1703): Developed compound
microscopes and observed cork cells, coining the term “cells”
• Cell Theory (1838-1839): Established by Schleiden and
Schwann, stating:
1. Cells are the smallest structural units of all living things
2. Cells are the functional units of all living things
3. All cells arise from pre-existing cells
Cell Diversity
• By number: Single-celled (bacteria, amoeba) to multi-celled
organisms (humans with ~37 trillion cells)
• By size: Bacteria are smallest (0.3-5.0 micrometers), nerve
cells are longest, bird eggs are largest
• By shape: Varies according to function - red blood cells are
circular for capillary passage, nerve cells are long for impulse
conduction
Why Cells Stay Small
Small cell size provides advantages:
• Faster communication between cell regions
• Higher surface area to volume ratio for better diffusion of
nutrients, wastes, and gases
• Easier repair of cellular damage
Cell Structure
A generalized cell has three main parts:
1. Cell membrane (plasma membrane) - controls what
enters/exits
2. Nucleus - control center
3. Cytoplasm - contains organelles
Plant cells additionally have a cell wall made of cellulose for structure
and protection.
The chapter emphasizes that despite their microscopic size, cells are
the fundamental units that make all life possible.
Cell Structure Overview
Cell Wall & Membrane:
• Plant cells have a rigid, non-living cell wall made of cellulose
that provides protection and shape
• All cells have a semi-permeable plasma membrane (cell
membrane) that controls substance movement in and out of the cell
Cytoplasm and Organelles
Cytoplasm: A semi-liquid substance occupying most of the cell volume,
where chemical reactions occur and organelles are embedded.
Key Organelles:
1. Endoplasmic Reticulum (ER): Network of membranes
throughout the cytoplasm, connecting cell membrane to nuclear
membrane. Appears rough when ribosomes are attached, smooth
without them.
2. Ribosomes: Small granules that synthesize proteins, either
free in cytoplasm or attached to ER.
3. Mitochondria: Rod-shaped “powerhouses” that produce ATP
energy through cellular respiration. Contain their own DNA.
4. Golgi Apparatus: Stacks of flattened membranes that
package and transport cellular materials, including enzymes and
hormones.
5. Lysosomes: Digestive organelles containing enzymes that
break down waste and foreign substances. Called “suicide bags”
because they can destroy damaged cells.
6. Centrosome (Animal cells only): Contains two centrioles that
help organize cell division.
7. Plastids (Plant cells only): Include:
• Chloroplasts: Green plastids containing chlorophyll for
photosynthesis
• Chromoplasts: Colored plastids (yellow, orange, red) in
flowers and fruits
• Leucoplasts: Colorless plastids that store starch
Nucleus
The control center of the cell containing:
• Nuclear membrane: Double membrane with pores
• Nucleoplasm: Liquid inside nucleus
• Nucleolus: Dense region involved in ribosome production
• Chromatin fibers: Thread-like structures containing DNA
that condense into chromosomes during cell division
Non-living Components
• Vacuoles: Fluid-filled spaces (larger in plant cells) that store
water and maintain cell pressure
• Granules: Small particles storing food materials like starch
and fats
Key Differences
Plant vs Animal Cells:
• Plant cells have cell walls, chloroplasts, and large vacuoles
• Animal cells have centrosomes and smaller vacuoles
• Both share common organelles like nucleus, mitochondria,
ER, ribosomes, and Golgi apparatus
The text emphasizes that each organelle has specific functions
essential for cell survival and that the number of chromosomes varies
by species (humans have 46 chromosomes).
Cell Theory and Basic Concepts
Definition: A cell is the basic structural and functional unit of all living
organisms, consisting of protoplasm (living substance) enclosed by a
cell membrane, with an additional cell wall in plants.
Key Principles:
• All living things are made of cells
• Every organism starts as a single cell
• All cells develop from pre-existing cells
• Cells are the unit of structure and function in living things
Cell Structure and Components
Common Components (found in both plant and animal cells):
• Plasma membrane, nucleus, cytoplasm, endoplasmic
reticulum, Golgi apparatus, mitochondria, ribosomes
Key Differences Between Plant and Animal Cells:
• Plant cells: Have cell walls (cellulose), chloroplasts, large
vacuoles, no centrosome
• Animal cells: No cell wall, have centrosome, smaller
vacuoles, no chloroplasts
Cell Types
Prokaryotic Cells (bacteria):
• No well-defined nucleus
• Single DNA strand
• Small ribosomes
• No membrane-bound organelles
Eukaryotic Cells (plants, animals):
• Well-defined nucleus with nuclear membrane
• Multiple chromosomes
• Larger ribosomes
• Various membrane-bound organelles
Cellular Activities
The text emphasizes that every activity in living organisms results
from cellular activity, including:
• Movement (muscle contractions)
• Digestion and nutrition
• Circulation and respiration
• Growth and reproduction
• Sensory functions
• Protection from disease
Protoplasm
Described as the total living substance of a cell (cytoplasm + nucleus),
containing elements like carbon, hydrogen, oxygen, nitrogen, and
phosphorus in the form of proteins, carbohydrates, fats, and mineral
salts.
Special Topics
Stem Cells: Brief mention of embryonic stem cells, tissue-specific stem
cells, and induced pluripotent stem cells (iPSCs) and their medical
applications.
The chapter concludes with review questions testing understanding of
cell structure, function, and the differences between cell types.
