1.1 The cells of multicellular organisms may
differentiate and become adapted for specific
functions. Tissues are aggregations of similar
cells; organs are aggregations of tissues
performing specific physiological functions.
Organs are organised into organ systems,
which work together to form organisms.
1.1.1 Large multicellular organisms develop systems for exchanging materials. During the development
of a multicellular organism, cells differentiate so that they can perform different functions.
126.96.36.199 A tissue is a group of cells with similar structure and function. Examples of
tissues include: muscular tissue, which can contract to bring about movement;
glandular tissue, which can produce substances such as enzymes and
hormones; epithelial tissue, which covers some parts of the body.
188.8.131.52.1 Organs are made of tissues.
One organ may contain several
tissues. The stomach is an organ
that contains: muscular tissue, to
churn the contents; glandular
tissue, to produce digestive
juices; epithelial tissue, to cover
the outside and the inside of the
184.108.40.206.1.1 Organ systems are groups of organs
that perform a particular function. The
digestive system is one example of a
system in which humans and other
mammals exchange substances with the
environment. The digestive system
includes: glands, such as the pancreas
and salivary glands, which produce
digestive juices; the stomach and small
intestine, where digestion occurs; the
liver, which produces bile; the small
intestine, where the absorption of
soluble food occurs; the large intestine,
where water is absorbed from the
undigested food, producing faeces.
2 B2.2.2 Plant Organs
2.1 Plant organs include stems, roots and leaves.
2.1.1 Examples of plant tissues include:
epidermal tissues, which cover the plant;
mesophyll, which carries out
photosynthesis; xylem and phloem, which
transport substances around the plant.
220.127.116.11 Leaves are adapted to absorbing sunlight for photosynthesis: chlorophyll, to absorb
sunlight; large surface area, to absorb more light; stomata, to let carbon dioxide diffuse
into the leaf; thin, short distance for carbon dioxide to diffuse into leaf cells; network of
veins, to support the leaf and transport water and carbohydrates.
18.104.22.168.1 The internal structure of a leaf is adapted to allow efficient photosynthesis: thin, waxy
cuticle made of wax, to protect the leaf without blocking out light; thin, transparent
epidermis, to allow more light to reach the palisade cells; layer of palisade cells on the
top surface, to absorb light; many chloroplasts in the palisade cells, to increase
absorption of light; spongy mesophyll inside the leaf, air spaces allow carbon dioxide
to diffuse through the leaf, and increase the surface area.