ch9 - xylem and phloem

Why do plants need transport systems

since they are multicellular they have a small SA:V so diffusion is too slow to meet their metabolic demands

What is the name of the transport system in plants

Vascular bundle

What tissues does the vascular bundle consist of

2 specialised tissues: xylem and phloem  

What is a Herbaceous dicot

plant with 2 seed leaves (cotyledons) where the vascular bundles are distributed differently depending on which part of the plant it is

What is another name for a dicot

A dicotyledonous plant 

What is the structure of vascular bundle in the roots (cross section)

-vascular bundle is found at the centre

> Xylem in middle forming an X shape

> Phloem found between the arms of the x shaped xylem

Why is the specific arrangement of the vascular bundle in the root important 

central arrangement provides strength to withstand pulling forces from the wind 

What is the structure of vascular bundle in the stem (cross section)

-the vascular bundles are arranged in a ring around the edge of the stem 

In each vascular bundle:

> xylem found on the inner side 

> phloem found on the outer side

Why is the specific arrangement of the vascular bundles in the stem important 

ring arrangement gives structural support preventing stem from bending 

What is the structure of the vascular bundle in the leaf (cross section)

-the vascular bundle form veins 

In each vascular bundle 

> xylem on top 

> phloem on bottom

Why is the specific arrangement of the vascular bundles in the leaf important

Supports the leaf & Maximises photosynthesis efficiency because:

> xylem closest to upper epidermis to supply water for photosynthesis 

> phloem is below to transport sugars made during photosynthesis

What are the 2 functions of the xylem 

To transport water and mineral ions from the roots up the plant 

Provide mechanical strength to the plant

name the 4 adaptations of the xylem

thick walls with lignin

dead xylem

no end walls

non lignified bordered pits

describe how these 4 adaptations enable xylem to carry out its job

-thick walls with lignin = woody and waterproof substance which provides mechanical strengthen to the cell wall so it can withstand high pressure of water 

-dead xylem = no organelles meaning its hollow tube - allowing smooth flow of water 

-no end walls = elongated tube - allowing smooth flow of water 

-non lignified bordered pits = allowing water and mineral ions to move out to surrounding cells when necessary

What does assimilates mean 

Refers to the products made during photosynthesis, mostly sucrose and amino acids 

What does source mean and name examples 

Source = organs of the plant where sugars are found/ originate from:

> leaves (makes sugars through photosynthesis)

> seeds and fruits (stores sugars that have been made)

What does sink mean 

Sink = all the other organs of the plant that use sugar for respiration to growth, carry out active transport, etc e.g. roots

What is the function of the phloem 

To transport dissolved assimilates, products made during photosynthesis (mostly sucrose and amino acids) from the source to the sink (translocation)

Why does the phloem transport sucrose rather than glucose 

Because sucrose is less reactive than glucose, it is less likely to be broken down and be used during cellular respiration 

How is sucrose obtained 

glucose is converted into sucrose and then it can be transported

name the 4 adaptations of the phloem

sieve tube elements

sieve plates with pores

phloem lacks organelles for smooth flow of assimilates 

companion cell

describe how these 4 adaptations enable phloem to carry out its job

-sieve tube elements = connected end to end forming a long sieve tube 

-sieve plates with pores = allows sugars and amino acids to flow through between sieve tube elements 

-phloem lacks organelles for smooth flow of assimilates 

-companion cell = keeps phloem alive & has many organelles e.g. large nucleus, mitochondria and ribosomes

Why is it so important that the companion cells has these organelles

Mitochondria - releases energy for active transport/translocation of substances into the sieve tube elements

Ribosomes - for protein synthesis

How are the companion cell and phloem connected 

by the plasmodesmata 

What is the plasmodesmata mean 

gaps that link the cytoplasm of two cells together allowing substances to cross between them 

What is the difference between plasmodesma and plasmodesmata 

Plasmodesma refers to a single gap 

Name the other structures that make up the root (going from outside to inner most)

root hairs > exodermis > epidermis > cortex > endodermis > vascular bundle