TRANSPORT IN PLANT CELLS

Plant transport systems are less complex than those of animals. Plants are less active so their cells do not need to be supplied with substances as quickly. The structures of plants also enable them to get enough oxygen to their cells by diffusion. Plants have two transport systems called The Xylem The Phloem

STRUCTURE OF XYLEM VESSELS Xylem vessels are: Hollow and dead with no cytoplasm or cellular components in a regular cell The end walls have disappeared and since they meet end to end, they form long tubes throughout the plant. Their walls are made of cellulose and lignin which is very strong.

FUNCTION OF XYLEM VESSELS Transport WATER from the roots of plants, up the stems and to the leaves. Strong lignin present helps to hold the plants upright. Wood is therefore mainly composed of lignin.

STRUCTURE OF PHLOEM TUBES Phloem is made of long hollow cells joined end to end, but their end walls have not completely broken down. The cells are living. Phloem tissue has seive plates, sieve tubes and companion cells with cytoplasm and organelles.

FUNCTION OF PHLOEM TUBES   Phloem tubes carry food materials made by chloroplasts found mainly in the leaves of plants, to the rest of the cells of the plant that do not readily photosynthesize.

VASCULAR BUNDLES Xylem vessels and phloem tubes are usually grouped close together in structures called vascular bundles.

VASCULAR BUNDLES In roots, vascular bundles are found in the centre. In stems they are arranged in a ring near the outside edge.

VASCULAR BUNDLES In leaves, they are found throughout and side by side (they collectively form the veins).

RECAP VASCULAR BUNDLES

MOVEMENT OF WATER THROUGH PLANTS

The movement of water through a plant can be broken down into five stages: Absorption of water by the root hair cells Movement of water across the root cortex to the xylem Movement of water up the xylem Movement of water across the leaf cells Evaporation of water from the leaves

SUMMARY Water moves from soilroot hair cellsroot cortex xylem up to leavesatmosphere

WATER UP THE XYLEM Water moves up the xylem by: Capillarity (along with adhesion and cohesion) Root pressure Transpiration pull All leading to mass flow.

CAPILLARITY Capillarity is how liquids travel up narrow tubes. The more narrow the tube, the faster the movement of water.

ADHESION AND COHESION Cohesion is the attraction of water molecules to one another so they can move together. Adhesion is the sticking of these water molecules to inner surfaces of the xylem vessels as capillarity carries them upwards.

ROOT PRESSURE Roots have a high concentration of sugars and a lower concentration of water. Since the soil has a higher water concentration, water constantly moves into roots helping to push water before it up the xylem to the leaves.

WATER ENTERING ROOTS

WATER ENTERING ROOTS

TRANSPIRATION PULL The leaves are constantly losing water. This water must be replaced and this creates a tension that “pulls” water up from roots and xylem.

WATER IN THE LEAF Water moves from cell to cells in the leaf, each previous cells having a greater water potential (more water) than the last. So a concentration gradient is made and water moves from cell to cell by osmosis until reaching the stomata to exit into the atmosphere.

TRANSPIRATION Transpiration is the evaporation of water from the leaves of the plant through the stomata which are more numerous on the underside of the leaf.

TRANSPIRATION STREAM This is the movement of water from roots to xylem to leaf.

TRANSPIRATION RATE This is how quickly water leaves the leaf. Factors affecting transpiration rate are: Wind Humidity Temperature Light intensity Water availability

FACTORS AFFECTING TRANSPIRATION

TRANSLOCATION

Translocation of Minerals and Organic Substances Transport of organic substances produced by photosynthesis transported to other parts of the plant. For growth or storage. Phloem is responsible.

Evidence of Phloem Translocation of Organic Substances Cut phloem releases sweet sap. Sugar content of phloem varies with environmental conditions just like photosynthesis.

Evidence of Phloem Translocation of Organic Substances Removal of a ring of phloem accumulates sugars above ring.

Radioactive 14CO2 given to plants, 14C carbohydrates found in the phloem. Aphids feeding on phloem, show presence of carbohydrates and amino acids in mouth.

STORAGE ORGANS OF PLANTS

Plants need to convert and store the products of photosynthesis for later use. Converted to sucrose for transport in phloem. Food stored as sucrose or starch.

Storage organs of plants can be: Underground stem Above ground stem Roots Underground leaves Fruits Seeds

UNDERGROUND STEM RHIZOME (ginger) CORM (dasheen)

UNDERGROUND STEM STEM TUBER (Irish potato) STEM TUBER (Irish potato)

ABOVE-GROUND STEM SUGARCANE CELERY

ROOTS TAP ROOTS (carrot) TAP ROOTS (turnip)

UNDERGROUND LEAVES BULB (onion) BULB (Lilly)

FRUITS

SEEDS ENDOSPERMIC (corn) NON-ENDOSPERMIC (cotyledonous) (red pea)

FLOWER CAULIFLOWER BROCCOLI

LEAVES LETTUCE CABBAGE