1.6 Appreciating a healthy cardiovascular system• The cardiovascular (cardio= heart, vascular = vessel) system consists of the

heart and all of the blood and lymphatic vessels in the body.• Cardiovascular diseases consists of:- Diseases of the heart- Diseases of the blood vessels• Most of deaths from cardiovascular diseases are from:(a) Coronary heart disease (heart attack)(b) Heart failure (the heart fails to pump sufficient blood to the vital organs,

which causes shortness of breath, fluid retention and fatigue)(c) Stroke (sudden loss of brain function when the blood vessels in the brain

rupture)(d) Diseases of the arteries such as arteriosclerosis and hypertension

• Major risk factors for cardiovascular diseases are high level of cholesterol, family history, age, cigarette smoking, obesity, diabetes mellitus and a sedentary lifestyle.

• The risks of contracting cardiovascular diseases can be reduced in the following ways:

(a) Limiting the consumption of unhealthy fats and cholesterol(b) Choosing low fat protein food sources(c) Eating more vegetables and fruits(d) Eating more whole grains(e) Avoid consuming excessively salty foods(f) Practice moderation and do not over eat(g) Getting sufficient exercise(h) Avoid smoking(i) Reducing stress

1.7 Understanding the Transport of Substances in Plants

The necessity for transport of substances in plants• Water is an important component of cells. It acts as a solvent and is often a

reactant in cell metabolism• Mineral ions are required for chlorophyll synthesis, healthy plant growth and

development• Organic food materials need to be sent to the growing regions. Storage

organs and other parts of the plant.• Water and minerals from the root need to be transported to the leaves

Vascular Tissue in Stem, Root and Leaf

• The vascular tissue of plants consists of:a) Xylem – gives support and mainly transport water and mineral

ions from the roots to the upper parts of the plantb) Phloem – transport organic food substances synthesised by the

leaves during photosynthesis to other parts of the plant

The structure of vascular tissue(1) Vascular Tissue in the Stem of a Dicot• The main tissue in a stem of a dicot are:(a) The epidermis(b) The cortex, which consists of collenchyma, chlorenchyma and

endodermis(c) The vascular bundle (xylem & phloem)(d) The pith

Vascular tissue in the stem of a dicot

• The vascular bundle in the stem of a dicot are arranged in a ring near the circumference of the stem

• Within each bundle, the xylem is located towards the centre of the stem and the phloem is located towards the periphery

• The cambium is sandwiched between the xylem and the phloem

• The cortex is located outside of the vascular bundle ring while the pith located inside the vascular bundle ring

Structure Characteristics

Cortex •Consists of collenchyma, parenchyma and endodermis

Epidermis •Consists of a single layer of closely packed living cells•The walls are thickened and are covered with a thin waterproof layer called the cuticle•The epidermis protects the underlying tissues

Collenchyma •These cells are found under the epidermis in young stems•Are alive, elongated, have thick cellulose cell walls and sometimes contain chloroplasts•Intercellular air spaces are either absent or are very small•FUNCTIONS: supports and strengthens the stem; and in the collenchyma with chloroplasts, photosynthesis takes place

Chlorencyhma •They are parenchyma cells that contain chloroplasts•The collenchyma tissue strengthens the young stem and the chloroplasts synthesise food during photosynthesis

Endodermis •The endodermis forms the innermost layer of the cortex•This is a single layer of tightly-packed rectangular cells bordering the vascular bundles of the stem•FUNCTIONS: stores starch; and allows solution to pass from the vascular bundles to the cortex

Structure Characteristics

Sieve tubes and companion cellsCambium •It is a layer of actively dividing cells lying between the xylem and

the phloem•Forms additional xylem and phloem

Tracheid •Conducts water and mineral salts from the roots to the shoots

Pith(medulla) •It occupies the large central part of the stem•It consists of thin-walled parenchyma cells with intercellular air spaces•FUNCTIONS:-Stores water & starch-Allows gaseous exchange through the intercellular spaces

2. Vascular Tissue in the Leaf of a Dicot• Vascular bundle consists of:(a) Xylem – which faces the upper epidermis(b) Cambium – which divides to produce xylem and phloem cells(c) Phloem – which faces the lower epidermis

3. Vascular tissue in the Root of a Dicot

• Vascular tissue packed in the centre• The vascular tissue is made up of xylem, phloem, and cambium• Xylem,phloem,cambium and the pericycle are know as the stele• Other structures observed in the dicot root include:(a) Root hairs – extension of the epidermal cells to increase the

absorption surface(b) Epidermis – absorption of water and minerals(c) Cortex – consists of the endodermis and the parenchyma cells

which store starch and sugar(d) Endodermis – active transport of certain minerals into the

xylem area(e) Pericycle – is a layer of parenchyma cells inside the

endodermis, from which lateral roots originate

Relating the structure of xylem to transport• Xylem has two functions:(a) Transports water and dissolved mineral salts from the roots to the

stems and the leaves(one way only)(b) Provides mechanical support for the plant

• The xylem tissue consists of these types of cells:(a) Vessel(b) Tracheid(c) Fibre(with rigid secondary cell walls for support and protection)(d) Parenchyma(food storage may take place in parenchyma cells)

(e) Only the vessels and the tracheids are CONDUCTING CELL

1. Vessels• Are dead cells which forming hollow tubes that connect the root to the

leaf• Lignin is a substance that is deposited on the vessel wall to strengthen it,

giving support to the stems and the stalks• The structure of the xylem vessel is adapted to transport water in the

following ways:(a) It is had CONTINUOUS LUMEN without any walls and protoplasm within it

to obstruct the flow of water and mineral salts(b) The walls are lignified to provide strength and prevent the vessel from

collapsing

2. Tracheids• Are dead cell when matured• Are long, slender cells with tapered, overlapping ends• Have smaller lumen than the xylem vessels• Have thick hard, lignified secondary cell walls• Have no sieve plates at the end of walls• Movement of water in tracheids:(a) Water moves sideways through the pits in adjacent tracheid cells before going upwards(b) The movement of water upwards is slower in tracheids than in the xylem vessels (where water flows upwards in a continuous vessel)

Relating the structure of phloem to transport

• Two main components:(a) Sieve tubes(b) Companion cells• May contain parenchyma(phloem parenchyma) and phloem

fibres

1. Sieve tubes• Is made up of a single row of elongated and thin-walled living cells called

sieve tube cells• A mature sieve tube:- Has only a thin layer of cytoplasm- Does not have nuclei or a central vacuole- Has also lost most of its other organelles• The cross-walls which separates sieve tube cells at both ends are called sieve

plates• are so-named because they are perforated by minutes pores like a sieve• Allow cytoplasmic connections between vertically-stacked cells which serve to

transport food by diffusion and active transport• depend on their adjacent companion cells for their many functions

2. Companion cells• One or more companion cells lie next to each sieve tube cell• Has a nucleus, endoplasmic reticulum, ribosomes and numerous mitochondria• Provide metabolic support for the sieve tube cells in the transport of

manufactured food

Removing a ring of phloem tissue from a plant• Phloem can be removed by cutting a ring of bark and removing it from the

stem• This ‘ringing’ cuts off the supply of food downwards beyond the ring• Food that is transported from the leaves down the stem in the phloem

accumulates above the ring• After a few weeks the bark above the ring swells(bulges).There is a

reduced growth below the ring• This shows that sugars are transported downwards in the phloem