2.3 Plant Tissues, Organs & Organ Systems

What are the plant tissues?

• Epidermal tissues

• Palisade mesophyll

• Spongy mesophyll

• Xylem and phloem

• Meristem tissue — grows at tips of roots and shoots

What are the features and function of epidermal tissue?

• Covers whole plant

• Covered with waxy cuticle → reduces water loss by evaporation

What are the features and function of palisade mesophyll tissue?

• Found underneath epidermal tissue

• Lots of chloroplasts → rapid photosynthesis

  • At the top of leaf → lots of sunlight

What are the features and function of spongy mesophyll tissue?

• Found underneath palisade mesophyll tissue

• Lots of air spaces → gases diffuse in and out of cells

What are the features and function of xylem?

• Found in roots, stems, and leaves

• Made up of dead cells joined together → creates continuous tube

  • Strengthened with lignin

  • Hole along tube — bordered pits

    • Lignin = strong and waterproof → water doesn’t leave

    • Except bordered pits — allows minerals to go to specific parts of plant

• Allows movement of water and mineral ions from roots → stem and leaves — evaporates and leaves plant

  • Transpiration stream

What are the features and function of phloem?

• Found in stem, roots, and leaves

• Elongated cells — holes in cell walls

  • End walls = sieve plates

• Many organelles from cells removed so cell sap moves through

• Food substances moved in both directions:

  • From leaves where they are made for use

  • From storage to parts of plant that need it

    • Translocation

What are the features and function of meristem tissue?

• Found at tips of roots and shoots

• Can differentiate → different types of plant cell

• Allows plant to grow

The leaf is a plant organ.

What tissues does it have?

• Epidermis

• Palisade and spongy mesophyll

• Xylem and phloem

• Guard cells surrounding stomata

What are guard cells?

• Cells that surround stomata

• Controls opening and closing of them — depending on water availability

What is the role of stomata and guard cells?

Control gas exchange and water loss

What are root hair cells adapted for? (2)

• Uptake of water by osmosis

• Uptake of mineral ions by active transport

What does phloem tissue do?

• Transports dissolved sugars from leaves → rest of plant

• For immediate use or storage

What is translocation?

Movement of food substances made in leaves up or down phloem — for immediate use or storage

What is transpiration?

• Loss of water from leaves and stems of plants

• Result of gas exchange — stomata are open

What factors affect the rate of transpiration? (4)

• Temperature

• Humidity

• Wind

• Light intensity

How does temperature affect the rate of transpiration?

• Increase in temperature → molecules move faster → evaporation happens faster → rate of transpiration increases

• Rate of photosynthesis increases → more stomata open for gas exchange → more water evaporates → rate of transpiration increases

How does humidity affect the rate of transpiration?

High relative humidity = reduced concentration gradient (between water vapour inside and outside of leaf) → slower rate of diffusion → decreased rate of transpiration

How does wind affect the rate of transpiration?

• More air moving away from leaf = lower concentration of water vapour surrounding leaf

• Steeper concentration gradient → increased rate of transpiration

How does light intensity affect the rate of transpiration?

• Increased light intensity → increased rate of photosynthesis

• More stomata open for gas exchange → more water evaporates → increased rate of transpiration

Why is there more stomata on the bottom of the leaf?

• Allows for gas exchange

• Minimises water loss by evaporation — lower surface is shaded and cooler

Describe the transport of water through a plant from the roots to the atmosphere. [3 marks]

• Water transported in xylem

• Water evaporates — through stomata

• A student investigated the volume of water lost from two plants of different species.

• Both plants were kept together.

• Figure 5 shows the student’s results.

Suggest one reason for the difference in the rate of water loss from the two plants in the first 2.5 hours. [1 mark}

Plant A has more stomata.

• A student investigated the volume of water lost from two plants of different species.

• Both plants were kept together.

• Figure 5 shows the student’s results.

Suggest two reasons why the rate of water loss in both plants changed after 2.5 hours. [2 marks]

It was warmer.