Science 10 - Chapter 9 Notes (Dec 2015) PDF

Science 10 – The Basis of Life Chapter 9.1: From Cell to Organism “Specialized and Organized” Unicellular Organisms vs. Multicellular Organisms Division of Labour o When a cell is specialized (performs a particular function), it is more effective and efficient toward compl...

Science 10 – The Basis of Life Chapter 9.1: From Cell to Organism “Specialized and Organized” Unicellular Organisms vs. Multicellular Organisms Division of Labour o When a cell is specialized (performs a particular function), it is more effective and efficient toward completing that function. o By comparison, a single-celled organism must multi-task and be able to do many jobs. Size o The surface area to volume ratio and related rate of diffusion restricts growth in unicellular organisms. o Efficient transport systems within multi-cellular organisms allow for growth. Interdependence of Cells o A single-celled organism is dependent on that one cell. o If a multi-cellular organism loses a cell, the entire organism will not die. However, a cell not functioning properly can still cause problems for the rest of the organism. Plant Structure – Cells, Tissues, and Systems Groups of cells performing the same function together are called tissues. Tissues contributing to the same function form organs. Organs work together as interconnected parts, and form a system.  The plant has two organ systems: o Shoot System - Everything above the ground. o Root System - Everything underground. Cells divide to grow and repair damage. This cell division is called mitosis. In plants, increase in size results from the cell division in growth areas called meristems. The root and shoot systems are made up of 3 types of tissues: 1. Dermal Tissue (epidermis) 2. Ground Tissue 3. Vascular Tissue Dermal Tissue Outer layer of cells that covers all herbaceous (non-woody) plants. Responsible for exchange of matter and gases into and out of the plant. Also protects the plant from disease. This is done by the cuticle (waxy substance), which resists attacks from micro-organisms and helps reduce water loss. Ground Tissue Found underneath epidermis, it makes up majority of plant. Provides strength and support to the plant (stem). Involved in food and water storage (roots). Location of photosynthesis (leaves). Vascular Tissue Responsible for transport of material, which occurs in xylem tissue and phloem tissue. Xylem Tissue o Conducts water and minerals from the roots to the leaves in plants. Phloem Tissue o Formed from long sieve tube cells (no nuclei), which are connected with companion cells (nucleated) that direct activity. o Transports carbohydrates and water from the leaves to other parts of the plant. Specialization in Plants Cells become specialized for a particular function and produce only the products needed for that function. Here are some examples: o Root hairs are tiny hair-like projections that aid in water and mineral absorption. o Formation of cuticles. o Guard cells form tiny pores called stomata allowing gas exchange. o Xylem is formed when cells die, creating a straw-like tube.  Science 10 – The Basis of Life Chapter 9.1: The Leaf & Photosynthesis The Chloroplast: A Unique Organelle Contain green pigment, chlorophyll. Found in the ground tissue of leaves and stems. The site of photosynthesis: o Light energy is absorbed by the chlorophyll and converted into chemical energy, stored in molecules of glucose, used in cellular Word Equation chlorophyll + light water + carbon dioxide glucose + oxygen Balanced Equation chlorophyll + light 6H20(l) + 6CO2(g) C6H12O6(aq) + 6O2 Plants also breathe... Cellular Respiration Breakdown of glucose molecules to release chemical energy that a cell can use. Word Equation glucose + oxygen carbon dioxide + water + energy Balanced Equation C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) + energy  Science 10 – The Basis of Life Chapter 9.2: Leaf Tissues & Gas Exchange Dermal Tissue Guard cells form tiny openings or pores called stomata that regulate gas exchange. Carbon dioxide and oxygen are able to enter and leave through diffusion. Most stomata are found in the lower epidermis on underside of leaf.  Opening of Stomata o Light strikes the leaf and stimulates guard cells to accumulate potassium ions. o The number of particles present in the guard cells increases, water enters by osmosis, and guard cells swell up under increased turgor pressure, opening the stomata. Closing of Stomata o Gasses dissolve in a film of water to pass across cell membranes. o Therefore, when the stoma is open, the plant is losing water. o The process of water vapour leaving the leaf through the stomata is called transpiration. o In conditions where water is not readily available, the guard cell becomes limp and the stomata closes. Ground Tissue Mesophyll – specialized ground tissue in a leaf, made up of thin walled cells containing chloroplasts. Two types of mesophyll: 1) Palisade Tissue Cells and 2) Spongy Mesophyll Tissue Palisade Tissue Cells o Found just below the upper epidermis, arranged in a manner allowing exposure to Sun’s rays. o Responsible for photosynthesis.  Spongy Mesophyll Tissue o Increased space between these cells allows for gas exchange by diffusion throughout the leaf. Vascular Tissue Provides the leaf with water for transpiration and photosynthesis, and removes sugars produced in photosynthesis. Xylem and phloem tissues are bunched together in a vascular bundle. Other sites of gas exchange in plants Not all gas exchange occurs in the leaf. Lenticels, like stomata, are natural openings (pores) found on stems, providing a pathway for gas exchange. h  Science 10 – The Basis of Life Chapter 9.2 – 9.3: Transport in Plants Cohesion and Adhesion Cohesion and adhesion are two properties of water that helps it to travel from roots to leaves. Cohesion o The attraction of water molecules to cling to each other, due to the polar nature (positive end of one molecule is attracted to negative end of another) of water molecules. Adhesion o The attraction of water molecules to molecules of other substances. This attraction allows water to pull itself up the plant. Root Pressure As a result of active transport in the roots, dissolved minerals are present and higher solute concentration is produced in the cell. Through osmosis, water is drawn into the cells, creating positive pressure that forces fluid up the xylem. Root pressure is only able to push water up a few metres. It is cohesion, adhesion, root pressure, and transpiration working together to transport water. From Root to Leaf: Water Transport in Plants Evaporation of water through stomata and lenticels through transpiration creates a tension or transpiration pull. When combined with cohesion, adhesion, and root pressure, water is able to be drawn up the xylem. Transpiration is dependent on temperature. Higher temperatures increase the rate of evaporation and cause rapid movement in xylem. The Effect of Tonicity on Plants Tonicity of the environment has an effect on osmosis and on the arrangement of structures in plant cells. Plasmolysis – shrinking of the cytoplasm and plasma membrane away from the cell wall due to the outflow of water in a hypertonic environment. A leaf will appear wilted or limp as a result of plasmolysis. From Source to Sink: Sugar Transport in Plants Phloem tissue is essential to the transport of sugar from the leaves to the rest of the plant, to enable cellular respiration. The leaves (place of photosynthesis) are referred to as the source, and the places where sugars are used are also known as the sink. Pressure Flow Theory At the leaf, phloem becomes loaded as companion cells use carrier proteins and active transport to take in sugar molecules form the sites of photosynthesis. Water moves into sieve cells by osmosis. Increased water pressure inside the sieve cells pushes the water and sugars through the phloem to the rest of the plant. Sugar molecules may be used in growth, respiration, or other life processes. The pressure differences produced by active transport and osmosis maintain a constant flow of food down the sieve tube.  Biology 10 – The Basis of Life Chapter 9.4: Control Systems Just as animals respond to internal and external stimuli, plants do the same. A plant needs water, carbon dioxide, and light for photosynthesis, and therefore responds to accommodate these needs. A plant’s behavioural response for growth is referred to as tropism. Tropisms can be positive (toward the stimulus) and negative (away from the stimulus). There are many types of tropism: o Phototropism – response to light o Gravitropism/Geotropism – response to gravity o Hydrotropism – response to water o Thigmotropism – response to contact o Thermotropism, sonotropism, electrotropism, chemotropism… Investigations of Phototropism Scientists responsible for formulating questions and conducting experiments: o Charles Darwin and son Francis: Which part of the plant detects and responds to the phototropic stimulus? o Peter Boysen-Jensen: What is the signal that initiates the phototropic response? o F.W. Went: What is the specific substance responsible for initiating the phototropic response?  The Darwins discovered that the tip of the plant was responsible for the detection of light. Boysen-Jensen proposed a chemical moving from the tip is what allowed communication with the area of elongation (phototropic response created by elongation of cells on side of leaf facing away from light). Went isolated the specific chemical that caused bending in the coleoptile shoot, a hormone called auxin. Hormones are chemical compounds manufactured in one area, then transported to another location, and has the ability to initiate a physiological response.  The Frits Went experiments isolated that hormones are chemical messengers for plants. Some plant hormones include: o Auxin – growth hormone that stimulates cell elongation o Gibberellin – affects stem elongation, fruit growth, and seed germination o Ethylene – ripening, senescence (aging) and leaf abscission (shedding). Produced in response to physiological stress. o Abscisic acid – closes stomata, slows growth. AP Topics – Taxis, Kinesis and Taxonomy Taxis & Kinesis The concept of tropisms (as it is limited to growth of an organism) was eventually replaced by two new concepts, taxis and kinesis which relate to success and survival of the organism. Taxis is defined as an automatic, directed movement toward or away from a stimulus. o Positive taxis is toward the stimulus, negative taxis is away from the stimulus. o Examples include:  Euglena, a photosynthetic protest, moves toward a light source  Male moths fly in the direction of pheromone detection in order to find a mate.  Fish often swimming in an upstream direction. Response to this stimulus aids in water moving through gills without swimming, orients the fish in the direction from which food will arrive, and prevents being swept away by current.  It’s important to realize that tropisms in plants are taxes. Kinesis is a random, undirected motion in response to stimulus. o Examples:  Cockroaches scattering in any direction when a light is turned on.  E.coli tumbles randomly, rather than swims in a straight line, when nutrients become depleted. Taxonomy - Kingdoms of Life Taxonomy is the branch of biology concerned with classification. It is a systemic, highly organized classification. It is human nature to classify and organize: o Caveman – edible vs. non-edible o Early taxonomists – plant vs. animal (2 kingdoms) o Eventually a system based upon binomial nomenclature (2 names) was developed by Swedish naturalist Carollus Linnaeus. o The Linnaean system has evolved into an organization system requiring 8-levels of hierarchy! It begins with the domains of life… Recently the system has been modified to categorize all life into 3 broad groups called domain. o Domain are based on genetics and highlight that most of the history of life on Earth has been about single-celled organisms, therefore cell-type is the biggest influence on domain. o The 3 domain are eubacteria (true bacteria), archaebacteria (ancient bacteria) and eukarya (eukaryotes).  Eubacteria: o Simple organisms lacking nuclei & membrane-bound organelles (prokaryotic) o Contain peptidoglycan in their cell walls o Heterotrophic or autotrophic o Examples include bacteria and cyanobacteria Archaebacteria: o Prokaryotic like eubacteria, but none have cell walls containing peptidoglycan. o Heterotrophic o Are generally extremeophiles exploiting environments like ancient earth conditions such as salt lakes, hot springs, animal intestines (acid and methane…) Eukarya: o Larger, more complex cells. Organisms either single-celled or multicellular. o Contain a nucleus and membrane-bound organelles. o Heterotropic or autotropic o Reproduce sexually or asexually o Includes plants, animals, fungi and protists  Recall the differences between prokaryotic cells and eukaryotic cells. o Prokaryotes are significantly different from eukaryotes.  Science 10 – The Basis of Life Biology AP Enrichment - Meiosis Why do we look like our parents? Each parent donates genes to their offspring via sexual reproduction. The genes combine to give different but similar looking offspring. Homologous chromosomes Humans have 46 chromosomes consisting of 23 homologous pairs. Each parent donates one chromosome to each of the 23 homologous pairs. I.e., half of an individual’s chromosomes come from the female parent while half come from the male parent. Homologous chromosomes are the same length and carry the same genes in the same location. Those genes could be different versions. E.g., imagine the homologous chromosomes carry the eye color gene but one produces blue eyes while the other produces brown. The exception is the sex chromosomes. For these, females have a homologous pair (XX) while males do not (Xy). The other chromosomes are called autosomes. Two types of cells in general Somatic cells – diploid (2n) body cells. Contain a complete set of chromosomes. Reproductive cells – haploid (n) sex cells. These cells are called gametes and contain only half the number of chromosomes. If one somatic cell is fertilized by another, the resulting zygote would contain twice the number of chromosomes. I.e., the chromosome number would double each generation. For this reason, the chromosome number must be reduced during the production of gametes. This way, one haploid gamete is fertilized by another and the resulting zygote is diploid. The zygote carries a complete set of chromosomes, half from the female parent and half from the male. Every cell in the resulting organism is diploid and arises by mitotic division of the original zygote. The main stages of meiosis are the same as those in mitosis Meiosis happens in two stages: Meiosis I and Meiosis II. The two cell divisions result in 4 haploid daughter cells. During Meiosis I (the reduction division) homologous chromosomes are separated. Meiosis I – Animation: http://www.biology.arizona.edu/Cell_BIO/tutorials/meiosis/meiosis1_movie.html In Meiosis II, sister chromatids are separated. Meiosis II – Animation: http://www.biology.arizona.edu/Cell_BIO/tutorials/meiosis/meiosis2_movie.html After the chromosomes are replicated, sister chromatids remain attached at the centromere. Also, homologous pairs (each consisting of two sister chromatids) remain close together. The four sister chromatids are called a tetrad and the process is called synapsis. During synapsis, the arms of chromosomes in a homologous pair become intertwined. Pieces of the homologous chromosomes break off and switch places. This phenomenon is called crossing over. This increases genetic diversity which results from sexual reproduction. Events contributing to Genetic Diversity Independent Assortment o The orientation of homologous chromosomes on one side of the metaphase plate or the other in Meiosis I is random. o The number of possible orientations is 2n, where n is the haploid number. For humans, the number is 223 = 8.4 million Random fertilization o Any of a male’s 8.4 million sperm can fertilize any of a woman’s 8.4 million eggs. The total number of combinations is over 70 trillion! Crossing over o When crossing over is considered, the number of combinations is nearly infinite. Genetic diversity contributes to evolutionary change If an offspring inherits a combination of genes that gives it a survival advantage, it is better able to survive and pass on its genes. This means the chance that the combination is passed on increases. As a result, there is an accumulation of favorable characteristics.  Science 10 – The Basis of Life Biology AP Enrichment - Mitosis General Info: Approximately 10 trillion cells in the human body all arose from a single cell by mitosis. For example red blood cells are made at the rate of one million per second! Cell division is called mitosis. For single celled organisms, mitosis increases the number individuals; for multi-celled organisms, mitosis adds to growth, differentiation and repair. Mitosis has two basic functions: i. Duplicate the cell ii. Ensure that each daughter cell has a complete copy of the DNA The basic steps are: i. Duplicate the DNA ii. Divide the chromosomes into two complete sets iii. Divide the cell into two daughter cells The cell cycle consists of mitosis (10%) and interphase (90%) Stages of the cell cycle (Interphase -P.M.A.T.-Cytokinesis) 1. Interphase a. Includes all cell activity between mitotic divisions during which the cell is preparing for division. This includes production of cytoplasm and organelles for two daughter cells. b. Each chromosome is duplicated and the resulting copies are called sister chromatids. They remain attached to one another at a region called the centromere. The whole structure is still one chromosome. Chromosomes are uncondensed during interphase. 2. Mitosis a. Prophase i. The chromosomes (which are now sister chromatids) shorten and thicken (condense) ii. Centrioles move to opposite poles of the cell iii. Spindle fibers are constructed to extend from the centrioles toward each chromosome iv. The nuclear membrane is dissolved b. Metaphase i. During late prophase chromatids begin to move toward the cell equator (equatorial plate) ii. At metaphase the chromatids are aligned at the equator (they are most visible at this stage) c. Anaphase i. Chromatids begin to move apart, toward opposite poles ii. Once separated, the chromatids are again called chromosomes  d. Telophase i. The chromosomes reach opposite poles of the cell ii. Spindle fibers dissolve iii. Nuclear membrane reforms at each end of the cell e. Cytokinesis i. The division of cytoplasm after separation of the chromosomes ii. In plant cells, a new cell wall forms to divide the two daughter cells iii. In animal cells, the cleavage furrow forms as the cell membrane is pinched inward to divide the cell into two daughter cells The whole process is summarized here: Mitosis Movie/Animation: http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/mitosis_movie.html