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Grade 9 Science SNC1D
Unit 1
The Power of Reproduction
Chapter 1
The Cell Cycle and Asexual Reproduction
1.1 The Cell: Understanding the Basic Unit of Life
1.2 Understanding the Cell Cycle
Cell Theory – Cell is the basic unit of life
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All living organisms are composed of one or more cells
Cells are the basic units of structure and function in all organisms
All cells come from previously existing cells
The activity of an entire organism depends on the total activity of its independent cells.
Inside the Basic Unit of Life
A typical cell has numerous membrane-bound organelles, specialized structures that perform specific functions in the
cell.
Chromatin: formed by DNA (holds the instructions to assemble the necessary substances for building the cell and
making it work)
Cell membrane: enclose the cell contents
Mitochondrion: transform energy for the cell
Nucleus: organelle bounded by a double-layered porous membrane
Nuclear membrane: encloses the cell’s genetic material or DNA (Deoxyribonucleic Acid)
Cytoplasm: supports the nucleus and other organelles, enclosed by the cell membrane.
Lysosome: break down food and digest wastes and worn-out cell parts
Endoplasmic reticulum: forms a series of canals, and materials are transported through these canals.
Golgi body: package useful materials and secrete them to the outside of the cell for use elsewhere in the organism
Vacuole: contain water, food, wastes, and other materials
Nucleolus: darker area within the nucleus that manufactures ribosome parts
Ribosome: contribute to the manufacture of substances important for cell function
Cell Wall: provides structure and support for the cell
Chloroplast: enable them to make their own food through the process of photosynthesis
Cell Cycle:
The process that ensures each new cell has a nucleus with a complete set of instructions (DNA) is called mitosis.
Before mitosis can begin, the nucleus must make a copy, or a replica, of its chromatin, so that there are two complete
sets of DNA. This step is known as replication. The replicated chromatin coils up to form double-stranded chromosomes,
which are joined in the middle by a centromere.
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The Phases of Mitosis in an Animal Cell
Phase 1: Prophase
-Double stranded chromosomes are large and dense
-nucleolus and the nuclear membrane disappear
-spindle fibres begin to form and stretch across the cell from centrioles.
Phase 2: Metaphase
-spindle fibres pulls the double-stranded chromosomes into a line across the middle of the cell
Phase 3: Anaphase
-spindle fibres begin to contract and shorten
-pulls the centromere apart, allowing one of each of the replicated strands to move to opposite ends of the cell
Phase 4: Telophase
-spindle fibres begin to disappear
-nuclear membrane forms around each set of chromosomes
-nucleolus appears
-single-stranded chromosomes start to uncoil into thin strands of chromatin
-ready to divide
-still one cell, but has two identical nuclei
Cell Division
In plant cells, a cell plate develops across the centre of the cell, forming a new cell wall between the two new cells.
# chromosomes is identical to original cell.