Download LS. 2 Notes

1
LS. 2
Cells
I. History of Cells
A. The invention of the microscope made it possible for people to discover
and learn about cells. A microscope is an instrument that makes small
objects look 100 times larger.
B. One of the first people to observe cells was the English scientist and
inventor, Robert Hooke. Hooke built his own compound microscope and
used it to observe the structure of thinly sliced pieces of cork. Hooke
noticed the spaces in the cork looked like tiny rectangular rooms and
called them cells.
C. Anton van Leeuwenhoek looked at drops of lake water, scrapings from
teeth and gums, and rain water from gutters. Leeuwenhoek found many
one-celled organisms and noted that many of them moved. He called
these moving organisms animalcules.
II. The Cell Theory
A. Three German scientists made important contributions to our knowledge
about cells. These scientists were Theodor Schwann, Matthias Schleiden,
and Rudolf Virchow.
B. Schleiden concluded that all plants are made of cells. He based this on
previous research.
C. Theodor Schwann concluded that all animals are made up of cells. Thus,
all living things are made up of cells
D. Rudolf Virchow proposed that new cells are formed only from cells that
already exist, “all cells come from cells,” wrote Virchow.
E. The Cell Theory is a widely accepted explanation of the relationship
between cells and living things. The Cell Theory states the following:
1. All living things are composed of cells.
2. Cells are the basic units of structure and function in living things.
3. All cells are produced from other cells.
III. Parts of a Cell
A. A cell wall is a rigid layer of non-living material that surrounds the cells of
plants and some organisms.
B. The cell membrane forms the outer boundary that separates the cell from
its environment. It controls what substances come into and out of the cell.
C. The nuclear envelope surrounds the nucleus and protects it.
D. The thin strands floating around the nucleus that contain genetic material
are called chromatin.
E. The nucleolus is a small object in the nucleus that is in charge of making
ribosomes.
2
LS. 2
F. Mitochondria are known as the power houses of the cell. They convert
energy in food molecules to energy the cell can use to carry out its
functions.
G. Endoplasmic reticulum’s passageways carry proteins and other materials
from one part of the cell to the other.
H. Ribosomes function as factories to produce protein.
I. Golgi bodies receive proteins and other newly formed materials from the
endoplasmic reticulum, repackage them, and distribute them to other parts
of the cell.
J. Chloroplasts capture energy from sunlight and use it to produce food for
the cell.
K. Vacuoles are the storage areas of the cell.
L. Lysosomes are small, round structures containing chemicals that break
down certain materials of the cell.
IV. Cellular Transport
A. In endocytosis, the cell engulfs some of its extracellular fluid, including
material dissolved or suspended in it. A portion of the plasma membrane
is invaginated and pinched off forming a membrane-bounded vesicle
called an endosome. Endocytosis removes portions of the plasma
membrane and takes them inside the cell.
B. Exocytosis is the opposite of endocytosis and is the release to a cell
surface of substances such as waste or secretions through vesicles.
V. Cell Division
A. Mitosis is the process by which a cell divides into two daughter cells,
each of which has the same number of chromosomes as the original
cell.
B. Meiosis happens in organisms that reproduce sexually, a process of
cell division during which the nucleus divides into four nuclei, each of
which contains half the usual number of chromosomes.