Unit 11.

Plants
They are all multicellular organisms: they are made up of many eukaryotic plant cells that form
groups to carry out specific functions.

Many plants contain vascular system: cells used for transporting water and minerals to different
parts of the organism. The vascular system is made of two types of tissues: xylem and phloem.

• Xylem: this tissue is responsible for transporting water and minerals from the roots up
through the plant to the leaves and other parts.
• Phloem: this tissue is responsible for transporting the nutrients (glucose) made through
photosynthesis to other parts of the plant where it is needed or stored.

Plants are autotrophs: they produce their own food by carrying out photosynthesis. To do this
they need sunlight, water and carbon dioxide. They produce glucose and oxygen. The green
colour of plants comes from chlorophyll. This pigment is essential to photosynthesis as it absorbs
the sunlight.

There are different types of plants:

1. Non-flowering plants: plants without seeds, flowers or fruits.

a. Byophytes (mosses), which don’t have roots, stem and leaves and don’t have
vascular tissue.
b. Pterydophytes (ferns), which have roots, stem and leaves and vascular tissue.
2. Flowering plants: plants with flowers and seeds. Some of them have fruit. They all have
vascular tissue and roots, stem and leaves.
a. Gymnosperms, their seeds grow inside a cone (not inside a fruit). This is because
the ovules (female gametes) aren’t enclosed inside the flower’s ovary.
b. Angiosperms, their seeds grow inside a fruit. This is because the ovules (female
gametes) are enclosed inside the flower’s ovary.
The cotyledon is the first leaf that a plant grows from a seed.
▪ Monocotiledons are plants that only have one cotyledon. They produce
leaves with parallel veins. They have flower parts in multiples of three.
▪ Dicotiledons are plants that have two cotyledons. They produce leaves with
branched veins and flower parts in multiples of four or five.

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 1. NON-FLOWERING PLANTS
Non-flowering plants do not have flowers, seeds or fruit. They usually live in moist environments and
reproduce by dispersing spores.

BRYOPHYTES (mosses)
Bryophytes are small, primitive land plants that need moisture and shade because they lack
vascular tissue and absorb water through their surface. They don’t have leaves, stems, or roots,
but instead have phyllidia, caulidia, and rhizoids. They reproduce with spores formed in the
sporangium (inside a capsule held by the seta). Bryophytes protect soil from erosion by growing close
together, help other plants grow, and provide food and shelter for various organisms.

PTERYDOPHYTES (ferns)

Pteridophytes have roots, a stem, and leaves (called “fronds”) with vascular tissue for
transporting food, water, and minerals. Roots absorb water and minerals and connect to underground
stems called rhizomes, which produce fronds. They live on land in moist environments as they need
moisture to reproduce. A sorus, a group of sporangia with spores, appears on fronds during
reproduction. Ferns are excellent indicators of ecosystem health, detecting changes in water quality
and being sensitive to air humidity and temperature, and are used to measure the effects of climate
change.

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 2. FLOWERING PLANTS
FLOWERING PLANTS

Flowering plants can live in all types of environments. They have vegetative organs that control their life
processes. They have reproductive organs that carry out the function of reproduction.

1. VEGETATIVE ORGANS

The vegetative organs are essential for maintaining life through the function of nutrition. They include the roots,
stem and leaves.

The roots fix the plant to the The stem contains xylem, which Stomata, the tiny green pores in
ground, they also absorb water transports water and nutrients green plant leaves, take in carbon
and minerals from the soil. from the roots to all parts of the dioxide and expel oxygen as part
Secondary roots sprout from the plant. The stem also contains of photosynthesis and gas
main root. Secondary roots grow phloem, which carries nutrients exchange. Water travels through
root hairs which help to increase produced in the leaves around the the plant and is expelled from the
the plant’s area of absorption. plant. The stem keeps the plant stomata in the process of
upright and can be rigid (woody) transpiration.
or flexible (herbaceous).

2. REPRODUCTIVE ORGANS

Flowers are the reproductive organs of flowering plants.

• The sepals (calyx) are green leaves which enclose

and protect the flower.
• The petals (corolla) are colored leaves that attract
pollinating insects. They also protect the reproductive
organs.
• The pistil (female reproductive part) is divided into
stigma, style and ovary. Inside the ovary are the
ovules (female gametes).
• The stamens (male reproductive part) is formed by
the filament and the anther. The anther contains
pollen grains (male gametes).

Flowers can be hermaphroditic (they have stamen and pistil) or unisexual (they only have stamens or pistil,
like gymnosperms).

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GYMNOSPERMS

Gymnosperms are a group of flowering trees and bushes that can exist in all types of climate,
especially cold ones, and often form large forests. Most gymnosperms are perennial: they do not lose
their leaves in winter.

Their seeds grow in cones, not in fruit. This happens because the ovules aren’t inside the flower’s
ovary. There are male cones and female cones, so they always have unisexual flowers.

ANGIOSPERMS

Angiosperms are the largest group of flowering plants and they can be found in lots of different
climates.

Their seeds grow inside a fruit. This is because the ovules are inside the flower’s ovary. There can be
unisexual flowers and hermaphroditic flowers.

Angiosperms are classified into monocotyledons and dicotyledons.

• Monocotyledons: Monocotyledon seed embryos have one cotyledon

(an embryonic leaf). They produce leaves with parallel veins. They have
flower parts in multiples of three.
• Dicotyledons: Dicotyledon seed embryos have two cotyledons. They
produce leaves with branched veins and flower parts in multiples of four
or five.

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FLOWERING PLANTS NUTRITION
Human beings and other animals take their food from plants and other living things. However, plants
are autotrophs, which means they make their own food. Plant nutrition involves a number of steps:

1. Roots: Absorb water and minerals from the

soil, forming xylem sap.
2. Xylem: Transports xylem sap from roots to
leaves.
3. Leaves: Chloroplasts containing chlorophyll
absorb sunlight for photosynthesis. Carbon
dioxide is taken in through leaf stomata, and
oxygen is released. Sunlight converts water
and carbon dioxide into glucose.
4. Phloem: Transports glucose (phloem sap)
from leaves to the rest of the plant.

Plant respiration involves absorbing oxygen and releasing carbon dioxide. It occurs both during the
day and at night. Photosynthesis, on the other hand, only occurs during the day and is the process
by which plants get nutrients (glucose or phloem sap) and release oxygen into the atmosphere.

FLOWERING PLANTS INTERACTION

Plants can't move like animals but can respond to external stimuli such as gravity, light, and water
through two types of responses: tropism and nastic movement.

1. Tropism: it’s the movement of a plant’s roots, stem, or leaves in relation to a stimulus. Can
be positive (towards the stimulus) or negative (away from the stimulus). Types:
Phototropism Hydrotropism Gravitropism
This is the This is the This is the
movement movement movement
towards or towards or with or
away from a away from a against the
source of source of force of
light. water. gravity.

2. Nastic Movement: it’s a rapid, reversible movements in response to stimuli. These

movements are not permanent and can be repeated. Types:
Photonasty Seismonasty
A common response to Some plants respond to touch
changes in light intensity is or vibration. Venus flytraps
that many flowers close up at close their leaves when insects
night. move on them.

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FLOWERING PLANTS REPRODUCTION
Plants can reproduce asexually or sexually (through the fertilization of gametes).

1) ASEXUAL REPRODUCTION (or vegetative reproduction). Vegetative reproduction is

common in both herbaceous and woody perennial plants. It allows the plants to survive harsh
weather and involves different types of stem modification:
Rhizomes are Stolons (or
horizontal, underground runners) are
stems modification that horizontal stems
allows new shoots to that grow above
grow (e.g. ginger) ground. They can produce new shoots and roots
along their length (e.g. strawberry)
Tubers are modified Bulbs are underground
underground stems that buds surrounded by
store nutrients for the modified leaves that
plant (e.g. potatoes) store nutrients for the
plant (e.g. onion)

2) SEXUAL REPRODUCTION. Sexual reproduction in plants requires flowers.

In angiosperms, pollination involves
transferring pollen from the stamen to the
pistil, typically by insects or wind. During
fertilization, the pollen grows a tube to the
ovule, resulting in the fusion of gametes and
embryo formation. The embryo is surrounded
by protective tissue, forming a seed. The
ovary matures into fruit, protecting the seeds
as the petals and stamen fall off. When the
fruit falls, it disperses seeds to reduce
competition, often aided by animals, wind, or
water. With the right moisture and
temperature, the seeds germinate and grow
into new plants.
Gymnosperms reproduce with cones. Male cones produce
pollen carried by the wind to female cones, where it fertilizes
ovules that develop into seeds. These seeds are then released
(without a fruit) and can grow into new plants.