Biology - Section 2 - Notes

7/29/2019 Biology - Section 2 - Notes

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Section 2

2.1: Plant Cells, Tissues and Organs

1. Cell specialization: theprocess by which cells develop from similar cells into cells thathave specific functions within a multicellular organismi) Cells start out the same and undergo cell differentiation at some point in their

development

a) Cell differentiation: a stage of development of a living organism duringwhich specialized cells form

ii) Specialized according to the set of proteins they contain2. Tissue: a cluster of similar cells that share the same specialized structure and function3. Organ: a combination of several types of tissue working together toperform a specific

function

4. Meristematic cell: an unspecialized plant cell that gives rise to a specific specialized celli) Also called permanent embryos

ii) Constantly producing more cells, which then specializea) These cells combine to form the three types of tissues found in the body:

i. Dermal tissue:a. Forms the outermost covering of the plants organsb. Protects the delicate inner tissues from damagec. Controls the exchange of substancesbetween the plant and

its environment

d. e.g., epidermal cellii. Ground tissue

a. Some of these cellsperform photosynthesisI)Theprocess ofphotosynthesiscan be broken down

into two stages:

A) Light reactionsI. Light dependent reactionneeds

photons to function

II. Produces ATP andNADPHB) Dark reactions

I. Light independent reactiondoesnot need photons to function

II. Takes in CO2and light reactionproducts

III. Produces G3PIV. 6CO2 + 6H2O + light energy

C6H12O6 + 6O2

b. Othersprovide support forthe plants body


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iii. Vasculartissuea. Performs the critical job oftransporting necessary

substances throughout the plant

I)Xylem cells:deadtubular cells laid end to end thattransport water and minerals from the roots to other

parts (down-up)

II)Phloem cells:livingtubular cellsjoined end toend that transport sugarfrom the leaves to other

parts (up-down)

b. Helps to provide physical support for the plants bodyiii) Plants form new organsperiodically throughout their lives

a) Meristems are located at the tips of roots and branchesi. Bud: a swelling of the stem that contains meristem for new, not

yet developed, tissues in organs

a.

Terminal bud: the location where a plants most activegrowth occurs near

b. Lateral bud:dormant, but has the potential to produce newbranches, leaves, and flowers

b) Cells in actively growing areas give off a hormone called auxini. Auxin controls the cells below and behind them

a. If the terminal bud is removed, cells in the lateral bud beginto divide and specialize

5. Four organs of plants:i) The leaf:

a) Primary task is toprovide a large surface area for photosynthesis to takeplace

b) If the leaves produce excess glucose than needed, it is converted intostarch and the leaves store it

c) The upperleaf:i. Epidermis: a sheet of dermal tissue whose main function is

protection

a. Cuticle: a waxy layerthat helps to reduce the amount ofwater that evaporatesfrom the leafs surface, secreted by

the epidermis

d) The middleleaf:i. Mesophyll tissue lies between the middle and lower surface,

which consists of:

a. Palisade cells: cells thatperform most of thephotosynthesis in the leaf, arranged in lines

I) Tops are designed to meet the Suns rays head on


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II)Very active, so they arepacked with mitochondriato perform cellular respiration

b. Parenchyma cells: a spongy layer below the palisade cellsthat forms a network with open spaces

I)Spaces contain the gases needed/producedbyphotosynthesis

e) The centreof the leaf:i. Vascular bundles:arrangements of xylem and phloem tissue

ii. Veins:dissect the interior of the leaf at regular intervals, formedby vascular bundles

a. Vessels meet the open spaces in theparenchyma tissueb. Xylem delivers water vapourto photosynthesizing cellsc. Phloem picks up sugars and delivers them to the rest of the

plant

d.

Veins ensure that every leaf cell can obtain water andnutrients

f) The lowerleaf:i. Made up of an epidermis that is crucial in gas exchangebetween

the leaf and the external environment

ii. Guard cells: cells scattered across the lower leafto allow gases tomove in and out by controlling the opening and closing of the

leafs pores

iii. Stoma (pl. stomata): the leafs pores, which are connected to theopen spaces in the parenchyma cells

iv. Transpiration: the evaporation of water from leaves, both ofwhich the guard cells and stomata contribute much towards

g) Chloroplasts:i. Able to change their shape and location in a cell to increase the

amount of light captured

ii. Thylakoid: a small sac within the chloroplast that contains light-trapping chlorophyll molecules, where photosynthesis occurs

a. Granum (pl. grana): a stack in which thylakoids arearranged

ii) The stem:a) Two main functions:

i. Providephysical supportii. Transport water, nutrients, and sugars

b) Contains most of a plants xylem tissuei. Forms vessels, whose thick cell walls remain after the cells die


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a. Lignin: a hard substance that fortifies the dead xylem cells,keeping the plant upright

b. Xylem vessels are grouped with phloem vessels, providingadditional support

c) Cambium: the thickening of the stemiii) The roots:

a) Two main functions:i. Anchora plant to the ground

ii. Allow it to take up water and minerals from the soilb) May also act as the plants storage areac) Parts of the root:

i. Root hairs: the main site of water and mineral absorptionii. Cortex cells: cells responsible forstarch storage; lots of space in

between so that water and minerals can flow to the endodermis

iii.

Endodermis:controls the transport of minerals between the cortexand vascular tissues

iv. Pericycle: the layer of tissue that surrounds the xylem and phloem;gives rise to branch roots

d) Two types of roots:i. Taproot: aplant with one main root that grows larger and thicker

than the rest

ii. Fibrous roots: aplant with roots that are all about the same sizeand spread out horizontally

a. Stabilize the soilb. Prevent soil erosion and landslides

iv) The flower:a) Reproductive organb) Contains two different types ofspecialized leaves

i. Pollenproduction(manufactures sperm)ii. Egg production

c) Theprocess of pollination:i. Animalspick up pollen from male parts

ii. Visit another plant of the same or another flower on the same plant;may transfer to the female parts

iii. Production of seeds, embedded in fruitsiv. Ethylene (a plant hormone) stimulates the ripening of fruits

6. Over400 viruses are known to infect plant cells, causing as many as 1,000 diseasesi) Tobacco mosaic virus/TMV: a virus that attacks the leaves of tomato, potato,

cucumber, and pepper plants


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ii) Gall: an abnormal growth of plant tissue caused by insects or micro-organisms(i.e., bacteria, viruses, and fungi)

a) Insects provoke gall development by injecting a chemical into the tissuei. The chemical alters which genes are turned on and offin the cells

ii. Gall develops where young insects are locatedb) Normally dont spreadto other tissues and are contained


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2.2: Plant Organ Systems

1. System: in biology, a group of tissues and organs thatperform specific functionsi) Root system: an organ system in a plant, which takes in water and minerals from

the soil and transports these substances to the shoot system

ii) Shoot system: an organ system in a plant, which supports the plant,performsphotosynthesis, and transports sap

2. The two systems are connected by the flow of useful and hormones through vascularbundles that contain xylem and phloem

i) Xylem tissue moves water and minerals from the roots to other parts forphotosynthesis

a) It does not use any energy stores because the cells die at maturityii) Phloem tissue moves the sugars resulting from photosynthesis to other plant parts

a) These cells activelypump substances to where they are needed in theplant

3. The importance of water:i) Too little water in the soil means:

a) Nutrient molecules cannot be taken up by the rootsi. They must be dissolved in water in orderto be absorbed and

moved up the xylem as sap

b) Photosynthesis cannot take placeii) Too much water in the soil means:

a) There will be a lack of oxygen for cellular respiration to occuri. The spaces between soil molecules would be filled with water

instead of oxygen molecules4. The importance of soil:

i) Plants are able to survive withoutit under certain circumstancesa) e.g., Greenhouse plants are grown in nutrient solutions, forming a

specific type of agricultural industry called hydroponics

5. Theprocess of substance absorption from the roots:i) Water and minerals enter the roots by osmosis towards the centre of the root

a) Root hair: a small extension of the roots epidermal cell membraneii) The substances travel through the cells orthrough the spaces surrounding the cells

until they reach the endodermis

a) The endodermis is surrounded by a waxy, waterproof substance thatprevents water from the passing in between the endodermis cells

i. Instead, they must pass through the cell membranes of theendodermis cells

iii) The substances move toward the xylem at the centre of the rootiv) The endodermis controls their passage from the cortex to the vascular tissuev) Finally, they arepushed into the xylem vessels


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6. Theprocess of water movement from the xylem and upwards:i) Via root pressure:

a) Mineral concentration in the xylem increases as the roots absorbnutrients

b) The high concentration accelerates osmosisc) Root pressure builds in the xylem vessels as water flows ind) Thepressure forces fluid up the xyleme) Root pressure is created under certain circumstances

i. e.g., At nighttime, when the soil is moistf) Responsible for only a few metres of water movement

ii) Via transpiration:a) Water from the soil enters in the xylem in the rootsb) Tension in the water column extends from the leaves to the rootsc) The water column in held togetherby cohesion

i.

Cohesion: the ability of water molecules to cling to each otherd) The water column is kept in place by adhesion

i. Adhesion: the tendency of water to stick to certain surfaces (i.e.,the wall of the xylem vessel)

e) Transpiration of waterfrom the leaves creates tension thatpulls on thewater column in the xylem

f) The rate of transpiration is controlled by the amount of water vapour inthe leaves

i. If there is a large amount of water:a. The guard cells open the stomata; water vapour moves out

ii. If there is a small amount of water:a. The guard cells relax, closing the stomata

7. Theprocess of moving nutrients:i) Glucose in converted into sucrose and other carbohydrates

ii) Sucrose is soluble in waterand is distributed via the phloemiii) Sucrose that travels to the roots is stored as starchiv) If the starch from the roots is needed, it is converted back into sucrose and is

transported as sap

v) Theprocess of moving maple sap:a) During early springtime, sap flows upwards from the roots through the

phloem to nourish growing leaves

b) The leaves mature and can produce their own glucosec) During summer and autumn, extra glucose produced by the leaves is

transported to other plant tissues or is stored in the roots

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Biology - Section 2 - Notes