A-Level Biology Cells

V. Organelles
A. Introduction to Organelles
 Organelles are specialized structures within cells that perform specific functions.
 Each organelle has a distinct structure and composition, and together they work together to
maintain the homeostasis of the cell.
B. Nucleus
 The nucleus is the largest organelle in most eukaryotic cells, and is the site of DNA
replication and transcription.
 It is surrounded by a nuclear envelope, which is a double membrane that contains nuclear
pores that allow for the transport of molecules in and out of the nucleus.
 The nucleolus is a region within the nucleus where ribosomal RNA is synthesized and
assembled into ribosomes.
C. Endoplasmic Reticulum (ER)
 The ER is a network of membranes that extends from the nuclear envelope throughout the
cytoplasm.
 The rough endoplasmic reticulum (RER) is studded with ribosomes and is involved in
protein synthesis and folding.
 The smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in lipid synthesis,
detoxification, and calcium storage.
D. Golgi Apparatus
 The Golgi apparatus is a stack of flattened membranes that receives proteins and lipids from
the ER and modifies and sorts them for transport to their final destination.
 It is divided into a cis face, which receives vesicles from the ER, and a trans face, which
sends vesicles to other parts of the cell.
E. Mitochondria
 Mitochondria are organelles that are responsible for cellular respiration, the process by
which cells generate energy in the form of ATP.
 They have an outer membrane and an inner membrane, which contains cristae that increase
the surface area for ATP synthesis.
 Mitochondria also contain their own DNA and ribosomes, which are similar to those found
in prokaryotic cells.
F. Chloroplasts
 Chloroplasts are organelles found in plant cells that are responsible for photosynthesis, the
process by which plants generate energy from sunlight.
 They have an outer membrane and an inner membrane, which contains thylakoids that
contain chlorophyll.
 Chloroplasts also contain their own DNA and ribosomes, which are similar to those found in
prokaryotic cells.
G. Lysosomes
 Lysosomes are organelles that contain digestive enzymes and are involved in the breakdown
of macromolecules, cellular waste, and foreign material.

,  They are formed by the fusion of vesicles from the Golgi apparatus and are important for
recycling cellular components.
H. Peroxisomes
 Peroxisomes are organelles that contain enzymes that are involved in the breakdown of fatty
acids and the detoxification of harmful substances.
 They are involved in the production of hydrogen peroxide, which is then broken down by
the enzyme catalase.
I. Cytoskeleton
 The cytoskeleton is a network of protein fibers that provides structural support and
maintains the shape of the cell.
 It is composed of microfilaments, intermediate filaments, and microtubules, which are
involved in a variety of cellular processes including cell division, movement, and
organization.


I. Introduction
 Importance of cells in biology
 Brief history of cell theory
II. Cell Theory
 The three components of cell theory
 The significance of cell theory in biology
III. Types of Cells
 Prokaryotic cells
 Eukaryotic cells
 The differences between prokaryotic and eukaryotic cells
IV. Cell Membrane
 The structure of the cell membrane
 The function of the cell membrane
 The importance of the cell membrane in maintaining homeostasis
V. Organelles
 The structure and function of the major organelles in eukaryotic cells, including:
 Nucleus
 Endoplasmic reticulum
 Golgi apparatus
 Mitochondria
 Chloroplasts (in plant cells)
 Lysosomes
 Peroxisomes
VI. Cellular Processes