structure and transport of a flowering plant · 7 ©the dublin school of grinds wesley hammond...

6th

Year

Biology

Higher Level

Wesley Hammond

Structure and Transport of a Flowering Plant

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Ref: 6/bio/h/wh/ StructureandTransportFloweringPlants

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Geography H Monday 17th - Friday 21st April 8:00am - 9:30am

German H Monday 17th - Friday 21st April 2:00pm - 3:30pm

History H Monday 10th - Friday 14th April 8:00am - 9:30am

Irish H Monday 10th - Friday 14th April 12:00pm - 1:30pm

Maths H Monday 10th - Friday 14th April 8:00am - 9:30am

Maths H Monday 17th - Friday 21st April 10:00am - 11:30am

Maths O Monday 10th - Friday 14th April 2:00pm - 3:30pm

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2 ©The Dublin School of Grinds Wesley Hammond

Contents

Structure of a Flowering Plant:

Structure of a Flowering Plant …………………………………………………………………….…3

Leaf Venation ………………………………………………………………………………………………..4

Structure of a Stem …………………………………………………………………………………….….5

Structure of a Root ………………………………………………………………………………………...6

Zones of a Root ………………………………………………………………………………………..........7

Xylem …………………………………………………………………………………………………………...8

Phloem ………………………………………….………………………………………………………………9

Location of Plant Tissue in Roots ………………………………………………………………….10

Location of Plant Tissue in Stems …………………………………………………………………11

To prepare and examine a transverse section (TS) of a dicot stem………………….12

Exam Questions …………………………………………………………………………………………...14

Structure of a Flowering Plant: 2004, 2006, 2007, 2008, 2009, 2012, 2014.

Transport in a plant: 2004, 2005, 2006, 2008, 2011, 2014.


Structure of a flowering plant:

Leaves:

• Leaves are attached to the stem at the

node.

• Stalk of leaf is called the petiole.

• Flat part of leaf is known as the blade or

lamina.


Leaf Venation:

1) Parallel venation:

• Veins run alongside each other.

• Found in monocot plants (grasses, daffodils)

2) Net or reticulate venation:

• Veins have branching pattern.

• Found in dicots (horse chesnut, rose and buttercup)

Function of the leaves:

• They can make food (photosynthesis).

• They exchange gases with the atmosphere (carbon dioxide and oxygen)

• Leaves store food (Lettuce)

• Leaves lose water to allow for transpiration.

Stem:

Herbaceous plants do not contain wood (no lignin)

Woody plants contain wood(have lignin)

The part of the stem between two nodes is called aninternode.

The tip of the stem has an apical bud (terminal bud)

The apical bud has a meristem which allows the stem togrow upwards.

The auxillary (lateral bud) produces new growth such as branches orflowers.


Structure of a stem:

NOTE: Lenticel is an opening for gas exchange found in stems of plants.

Functions of a stem: 1) Support the aerial parts of the plant.

2) Transport water and minerals from the roots to the leaves.

3) Transport food from the leaves to the roots

4) Carry out photosynthesis (if it is green)

5) May store food

http://www.google.ie/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=1Y_CDTeJko2zhM&tbnid=-BnR1cFh86AaDM:&ved=0CAUQjRw&url=http://science.howstuffworks.com/dictionary/plant-terms/stem-info.htm&ei=p_rGU9ecCeK57Ab7-IH4BQ&bvm=bv.71126742,d.ZGU&psig=AFQjCNFE_dsYS3g1OE5dDhbGHbr0ykzLJg&ust=1405635617907133


A closer look at the structure of a stem:

A = apical bud

B = Leaf scar

C = Scale scar

D = Lateral bud

NOTE: A scale scar shows the location of the previous

apical bud (distance between the scale scars indicates the

amount of growth that year).

How old is the stem above? 4 years

Roots Types of roots:

1) Tap roots

2) Fibrous roots

Tap Roots:

Tap roots consist of a main root called the primary root

or tap root.

Secondary roots appear from the tap root.

Found in dicots (dandelions ash trees)

Fibrous roots:

Consist of lots of equally sized roots.

Found in monocots (grasses and daffodils)


Functions of roots:

1) Anchors the plant in the soil

2) Absorbs water and minerals from the soil through its root hairs.

3) Store food in some plants (carrots and turnips)

What are the zones in a root?

1) Zone of protection

2) Meristematic zone (cell production)

3) Zone of elongation

4) Zone of diiferentiation

Zone of protection:

Root caps protect the root cells as they grow inthe soil.

Meristematic zone (Cell production):

This zone allows the roots to grow by producingnew cells.

A meristem tissue is capable of mitosis.

Meristems are found in the shoot tip and root tip.

Zone of elongation:

The cells in this zone grow longer by using plant growth regulators(auxins).

Zone of differentiation:

Consist of three different types of tissue:

1) Dermal tissue: protects the plant.


2) Ground tissue: support and photosynthesis (Found between the dermal

tissue and vascular tissue).

3) Vascular tissue: has xylem and phloem which transports materials.

Xylem transports water and minerals.

Note: Xylem is narrow to help the transport water.

Phloem transports food.

A detailed look at the structure of xylem tissue:

Xylem tracheids: • Long• Tapering• Hollow• Have pits

The pits allow water and minerals to move from cell to cell.

NOTE: Found in coniferous trees.

Xylem vessels:

• Tubular• They have a continuous tube• Have pits


Features of Xylem:

• Have lignin (gives strength)

NOTE: Lignin forms wood in trees.

Function: transport water and minerals.

Location: found in stems, leaves, roots and flowers.

A detailed structure of phloem tissue:

• Consists of sieve tubes and companion cells.

Sieve tubes: Long, tubular, with no nucleus

Companion cells: Have a nucleus which controls the activities of a sievetube and the companion cell.

Note: Xylem and phloem are found in vascular bundles in the leaf and stem.

Differences between xylem and phloem


Location of plant tissues in roots:

The phloem and xylem are located at the centre of root. Dermal tissue is found on the outside epidermis layer on the root and root

hairs.

What is an easy way to distinguish the TS of a root compared to TS of a stem?

The root has root hairs.

LS of a stem:

Location of plant tissue in stems:

TS of dicot stem


Vascular bundles in stem (xylem and phloem):

Monocotyledons and Dicotyledons

What is a cotyledon?

A cotyledon is a seed leaf which stores food for the seed.

• Monocots : daffodils, tulips, grasses and cereals

• Dicots : beans, peas, peanuts, sunflowers, roses, oak tree and ash tree.

Differences between monocots and dicots


To prepare and examine a transverse section (TS) of a dicot stem

1) Pick a non woody herbaceous plant which has a soft stem (e.g.sunflower, begonia) It is easier to cut.

2) Cut a short section of stem between two nodes using a scalpel.

3) Wet blade (reduces friction) and cut thin sections of the stem (cut awayfrom finger to prevent injury)

4) Cut sections at right angles to the stem.

Note: use a silt in some elder or carrot in case stem needs to be held into place. 5) Store sections in a clock glass with water (prevents stem from

dehydrating).

6) Place a thin section of stem onto a microscope slide using a forceps orpaint brush (allows light to pass through it easier).

7) Add a cover slip to slide at angle (eliminates bubbles).


8) Observe the slide under low power (x 100) and then under higher power(x 400).

NOTE: you could use a stain (iodine) to make them more visible.

Results:


Exam Questions: Exam paper 2004, Question 8:


Solutions 2004, Question 8:

Exam Paper 2006, Question 14c:

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Solutions 2006, Question 14c:

Exam Paper 2007, Question 6:



Exam paper 2008, Question 14c:





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Exam Paper 2014, Question 14b:

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Solutions 2014, Question 14b:


Transport in

Flowering Plants


Why plants need transport?

Plants need to be able to transport water, carbon dioxide, oxygen andminerals.

How do roots of plants take in water from the soil?

Root hairs absorb water by osmosis.

NOTE: Osmosis is the movement of water across a semi permeable membrane from a region of high water concentration (in the soil) to a low water concentration (in the root).

How are root hairs adapted for water absorption?

• Root hairs have thin walls (helps them to absorb water).

• Root hairs occur in large numbers (large surface area).


Movement of water into xylem:

• Water diffuses from the root hair into the ground tissue.

• It then diffuses from ground tissue into the xylem in centre of root.

How do the roots of plants absorb minerals?

• Plants require minerals to function (calcium, magnesium)

• Minerals are absorbed from the soil by root hairs in a process calledactive transport (requires energy)

• Root hairs have lots of mitochondria to supply energy.

How does water move up through a plant in the xylem?

Water moves up through a plant in two different ways:

1) Root pressure

2) Transpiration

Root pressure

Water taken in by the roots by osmosis causes a build up of waterpressure.

This root pressure pushes water up through the xylem

Note: Does not fully explain how water travels up large trees


Transpiration:

Transpiration is the loss of water vapour from the leaves of the plant.

Transpiration occurs through the stomata of a leaf (openings on the underside of a leaf).

How the Cohesion Tension model helps explain transpiration and the upward movement of water:

Cohesion Tension model • Allows large amounts of water to move quickly from roots to leaves in

warm conditions.

• Can move 220 litres in one hour up through a plant.

• This model was put forward by Henry Dixon and John Joly (IrishScientist in Trinity College).

• Cohesion: the sticking of water molecules to each other.

• Adhesion: when different molecules stick together (water sticks to the wall of the xylem)

Steps involved in the Cohesion Tension model:

1) Water evaporates from the xylem out through the stomata into the air(transpiration).

2) During transpiration each water molecule is pulled through the xylem.

3) Due to cohesion the next water molecule is pulled along by the one infront of it.

4) Xylem are adapted for movement of water because they are narrow.


5) When the water column in the xylem is stretched it is said to be undertension.

How is xylem adapted for transporting water?

It is narrow. It has lignin. Has pits.

Control of transpiration in leaves 1) Leaves have cuticle which does not allow water to pass through (cuticle

thicker on upper surface as this side is exposed to the sun)

2) Stomata are located on lower surface of leaf to reduce water loss (moreevaporation would occur on upper surface).


3) Each stomata is surrounded by two guard cells. The stomata can open orclose by the guard cells changing shape.

NOTE: Stomata are normally open during the day to allow gas exchange for photosynthesis. They close at night to reduce water loss.

The following environmental factors affect stomata opening or closing:

1) Plants lose too much water2) High temperatures3) High wind4) Carbon dioxide concentration

NOTE: Plants do not grow well in dry conditions because the stomata will remain closed for long periods.

How does CO2 concentration control stomata opening or closing?

High concentration of CO2:

• High levels of CO2 cause stomata to close.

• Photosynthesis rate decreases in the evening causing the build-up of CO2.

Low concentration of CO2:

• Low levels of CO2 cause the stomata to open.

• When photosynthesis begins in the morning CO2 is absorbed by themesophyll cells (ground tissue).


SUMMARY: High concentration of CO2 Stomata close

Low concentration of CO2 Stomata open

How do stomata open or close?

• Guard cells open and close the stoma by changing shape.

• When water enters the guard cell by osmosis, they swell and becometurgid.

• This causes the guard cells to buckle outwards creating a gap betweenthe guard cells.

• When the guard cells lose water they shrink, which causes the stoma toclose.

Gas exchange in a leaf:

Carbon dioxide:

Stomata helps with gas exchange. Large number of stomata increases theamount of gas exchange.

Carbon dioxide diffuses into the mesophyll of the leaf (ground tissuewhere photosynthesis takes place)

Oxygen:

Oxygen diffuses from the mesophyll of leaf into the air spaces and out ofthe stomata.

Water vapour:

Water vapour also diffuses out of the leaf through the stomata(transpiration)


Gas exchange in stems:

Lenticels are opening in the stem that allow gas exchange.

Normally oxygen diffuses inwards through a lenticels (needed forrespiration) and carbon dioxide diffuses outwards.

Food storage organs in plants:

Modified roots:

• Dicot plants can have large tap roots to store food (starch).

• This food is used to produce flowers, seeds and fruits.

Example: Carrots, Turnips

Modified stem:

• Potato plants produce an underground stem to store food (starch).

• These swollen stems are called tubers.

Modified leaves:

Onions, daffodils and tulips all produce a bulb.

What is a bulb?

• A bulb is an underground stem that has swollen fleshy leaves to storefood.

• The bulb is protected by a dry scaly leaf on the outside.



Exam Paper 2005, Question 14a:

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Solutions 2005, Question 14a:


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Exam Paper 2008, Question 14a:

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Exam paper 2008, Question 14a:

Exam Paper 2011, Question 15b:

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Solutions 2011, Question 15b:


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structure and transport of a flowering plant · 7 ©the dublin school of grinds wesley hammond...

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