Science 9 Biology Notes - Answer Key PDF

# Biology: The Cell ## Cell Theory - All living things are composed of cells. - Cells come from other cells - Cells are the smallest unit of life Each organelle in the Cell performs a different task. In most cells many of the same organelles perform the same function, whether in a plant cell or a...

# Biology: The Cell ## Cell Theory - All living things are composed of cells. - Cells come from other cells - Cells are the smallest unit of life Each organelle in the Cell performs a different task. In most cells many of the same organelles perform the same function, whether in a plant cell or an animal cell. ## Parts of the Cell: - **Cell Membrane:** Thin outer layer that controls the flow of materials into and out of the cell. - **Cytoplasm:** Watery substance contains the organelles (specialized cell parts) in the region between cell nucleus and the cell membrane. - **Nucleus:** Controls all cellular function including movement, growth, life functions; contains DNA. - **Nucleolus:** Organelle that makes ribosomes. - **Nuclear Membrane:** Contains the contents of the nucleus. - **Nuclear Pores:** Openings in the nuclear membrane that allows genetic materials to pass through. - **Vacuole:** Large membrane bound sac that regulates water. - **Vesicle:** Membrane-covered sac formed by the endoplasmic reticulum. Vesicles carry new proteins to the Golgi body - **Endoplasmic Reticulum (ER):** Membrane network which act as a transport system for the materials made in the cell. - **Golgi body:** Sorts and packages proteins. - **Mitochondria:** Converts chemical energy in sugar to ATP for the cell. "Power House" of the cell. - **Ribosomes:** Assemble proteins. - **Proteins:** Important building blocks for cells. ## Animal Cell Vs. Plant Cell | Animal Cell | Plant Cell | |---|---| | **Membrane**| **Cell Membrane**| | **Cytoplasm (organelles)**| **Cytoplasm**| | **Nucleus**| **Nucleus**| | **Vesicles**| **Vacuole**| | | **Cell Wall** | | | **Chloroplast** | | | **Large water vacuole** | ## Features Unique to Only Plant Cells: - **Chloroplasts:** Trap energy from the Sun to make sugar - food for the plant. - **Cell Wall:** Tough, rigid layer that surrounds the cell membrane, provides support and structure. - **Large vacuoles:** Plant cells are equipped with a large vacuole for water storage - **Photosynthesis:** Process where plants make sugar and oxygen. $Carbon\ dioxide\ +\ water\ +\ sunlight\ \rightarrow\ glucose\ +\ oxygen$ $CO_2 + H_2O + energy \rightarrow C_6H_{12}O_6 + O_2$ - **Cellular Respiration:** Is the process where cells use this food to use energy $C_6H_{12}O_6 + O_2 \rightarrow CO_2 + H_2O + energy$ $Glucose \ + oxygen \rightarrow\ carbon\ dioxide\ +\ water\ +\ energy$ # Biology: The Nucleus and DNA - The nucleus contains DNA (Deoxyribonucleic acid). - DNA is the molecule that has the master set of instructions for how cells function, what they will produce, and when they will die - DNA always remains in the nucleus. - DNA has the genetic code for proteins. - These proteins are enzymes which allow our body to do many functions. - Enzymes are special proteins that control chemical reactions in our bodies such as: respiration, digestion, cell growth and cell repair ## Structure of DNA - DNA looks like a twisted ladder - two strands wrap around each other in a coiled shape called a helix - The sides of the DNA ladder are made of sugar and phosphate ($PO_4)^{3-}$ - The steps of the ladder are made of four nitrogen bases. - Adenine (A). - Guanine (G). - Cytosine (C). - Thymine (T). - The two strands that make up the DNA double helix are paired together. - Each half of the DNA ladder is made up of complementary strands. - The bases join in a specific way - A always joins with T - C always joins with G - Looks like a zipper **Bases:** A, T, G, C - The series of "letters" (bases) along one side of the DNA ladder = Code. - One Gene can be several hundred "letters" (bases) long - All the letters make up a genetic code for the organism - It is the order the letters are arranged that determines the words in the coded message within each gene. ## Practice Problems: **Find the complementary DNA strand:** - T G C G C A T T G A C - A C G C G T A A C T G - A C C G T T C A A G G - T G G C A A G T T C C - Each group of 3 nucleotides will code for 1 letter (amino acid). - These amino acid link together to form proteins. - TGC could code for amino acid lysine. - CCC could code for amino acid glycine. - ATG could code for amino acid cytosine. **Each amino acid links to form a protein chain.** # Biology: The Cell Cycle - Due to the loss and death of cells, the body must replace cells constantly. A good example of this is human skin - each day millions are shed. ## Cell Replacement and Development: Here are some examples of the typical time it takes to replace cells in different parts of your body (Do NOT memorize these): - **Brain Cells:** Every 30-50 years. - **Red Blood Cells:** Every 120 days. - **Stomach Lining Cells:** Every 2 days - **Intestinal Lining Cells:** Every 3 days. - **Liver Cells:** Every 200 days. - **Skin Cells:** Every 20 days. The life of a cell is divided into 3 stages known as the cell cycle. These are: - **Interphase.** - **Mitosis.** - **Cytokinesis.** ## The Cell Cycle in More Detail: - **Interphase:** Cell carries out normal cell functions. - **Mitosis:** The nuclear contents are divided and split into two equal parts. - **Cytokinesis:** The separation of two nuclei and cell contents into 2 new cells. ## Interphase: - The longest cell cycle stage - this is when the cell performs normal cell functions and grows. - For example, an intestinal lining cell absorbing nutrients, or a red blood cell carrying oxygen. - In late interphase, DNA copies itself in the process of replication. 1. The DNA molecule unwinds with the help of an enzyme. 2. New bases pair with the bases on the original DNA A->T, C->G 3. 2 new identical DNA molecules are produced. # Biology: Mitosis - Cells reproduce or make more cells by a process known as cellular replication. - Cell theory states that cells form from other cells. - Because the body is constantly losing cells, these cells must be constantly making new cells in a process called mitosis. - The process in which 1 divides into 2 new IDENTICAL cells - This type of reproduction which involves only 1 parent cell forming two new daughter cells is known as asexual reproduction. - All body cells divide using mitosis (Body cells include skin cells, muscle cells, brain cells, eye cells, etc.) - We will see later that our sex cells (sperm and egg) use a different process to divide (meiosis). ## CELL CYCLE - **Interphase** - **Mitosis** - **Cytokinesis** - **Interphase:** When a cell is growing and preparing for reproduction. - **At the end of interphase, the cell continues to grow and make proteins in preparation for mitosis and cytokinesis.** - **During interphase, the cell must replicate its DNA.** - **Replication is when a copy of the cell's DNA is made.** - **At this stage there is 2x the amount of DNA present in the cell.** - **(a) shows a chromatid/chromosome** - **(b) the chromatids are replicated to make a replicated chromosome, also known as sister chromatids** ## ORGANELLS USED IN MITOSIS: - **Centrioles** - are organelles that organize spindle fibers. - **Spindle fibers** - connect to each of the sister chromatids. - As the cell divides, therofibens they pull the sister chromatids toward each end of the cell (poles) - **Mitosis is the shortest part of the cell cycle where the nuclear contents divide and 2 daughter nuclei are formed.** ## Interphase - **Mitosis** - **Prophase (P)** - **Metaphase (M)** - **Anaphase (A)** - **Telophase (T)** - **Cytokinesis (C)** - **As the nucleus prepares to divide, replicated DNA in the interphase joins to form sister chromatids joined by a centromere.** - **INTERPHASE:** Cell is growing and DNA is replicated. - **DNA is not yet observable because its loosely coiled.** - **MITOSIS → What are the steps that need to occur BEFORE the cell divide?** - **Grow** - **Replicate DNA** - **Make enough organelles** # Biology: Mitosis Part 2 - **Mitosis is the shortest stage of the cell cycle and is the process where the cell's nucleus divides.** - **When the cell divides, 2 daughter nuclei (plural of nucleus) with the same number of chromosomes as the original cell are formed.** **Remember: during interphase, the DNA molecules replicate to form sister chromatids of a chromosome (those chromotids are joined by the centromere).** ## MITOSIS: - **Prophase** - **Metaphase** - **Anaphase** - **Telophase** ## Early Prophase: - **Replicated chromosomes start coil up and become visible under microscope.** - **The nuclear membrane breaks down and the nucleolus disappears.** - **Centrioles move to opposite poles of the cell.** - **Spindle fibers form from the centrioles** ## Late Prophase: - **Spindle fibers attached to the chromosomes at the centromere (ready to pull them).** ## Metaphase (middle) - **Chromosomes line up along the equator (middle) of the cell (due to the tugging of the spindle fibers)**. ## Anaphase (apart) - **Spindle fibers contract and shorten to pull the centromere apart. Sister chromatids get pulled to opposite poles (ends) the cell.** ## Telophase (two) - **Spindle fibers disappear.** - **Nuclear membrane re-forms and nucleolus appears**. ## Cytokinesis: (not part of mitosis) - **The cell divides producing 2 new daughter cells that are identical to their parent cell.** - **In animal cells, the cell's cytoplasm pinches in to divide the cell.** - **In plant cells, a cell plate forms along the center of the cell to divide it into two.** ## MITOSIS SUMMARY: | Stage | Description | |---|---| | **Interphase** | | | **Prophase** | Chromosomes replicate | | **Metaphase** | Chromosomes align at middle of cell | | **Anaphase** | Separated chromosomes pulled apart | | **Telophase** | Microtubules disappear, cell division begins | | **Cytokinesis** | Two daughter cells both have the same number of chromosomes as parent cell. |