4.4 Making use of biodiversity

Question 1

Lignin, Lignified

Answer 1

A polymer found in some plant
cell walls. The main component of plant cell
walls is cellulose. In sclerenchyma and xylem,
the cellulose is impregnated with lignin. Lignin
makes the walls stronger and more able to resist
the forces on them. However, it also prevents water and salts getting through. As a result of
being lignified the cell dies.

Question 2

Chloroplast, Chloroplasts

Answer 2

A chlorophyllcontaining
organelle found in the cells of plants
and certain other organisms such as algae.
Photosynthesis, the process in which light
energy is converted to chemical energy, takes
place inside chloroplasts.

Question 3

Ribosome

Answer 3

A small organelle made of RNA and
protein found either free in the cytoplasm or
attached to the membranes of the rough
endoplasmic reticulum. Protein synthesis takes
place on ribosomes.

Question 4

Tonoplast

Answer 4

Membrane that surrounds a vacuole.

Question 5

Smooth endoplasmic reticulum, Smooth ER

Answer 5

A
network of interconnected sacs in the cytoplasm
of a cell. These sacs are surrounded by
membranes. Unlike rough endoplasmic
reticulum, smooth endoplasmic reticulum does
not have ribosomes attached to the outer
surfaces of these membranes. Smooth
endoplasmic reticulum makes lipids.

Question 6

Golgi apparatus

Answer 6

An organelle consisting of a
series of flattened sacs, each one enclosed by a
membrane. These membranes are continually
being formed on one side and pinched off into
vesicles on the other. Functions of Golgi
apparatus include processing, packaging and
secretion of proteins, secretion of the
carbohydrates, which form cell walls in plants,
and formation of lysosomes.

Question 7

Amyloplast

Answer 7

An organelle found in plant cells
which stores starch. Each amyloplast consists of
a tiny grain of starch surrounded by a doublelayered
cell membrane.

Question 8

Cell wall

Answer 8

A rigid layer surrounding a cell.
Bacteria, fungi and plant cells have cell walls.
Animal cells do not. In plants, the most abundant
substance in the wall is cellulose. The cell walls
of bacteria and fungi do not contain cellulose.
They are made of other substances.

Question 9

Cell membrane

Answer 9

A membrane found either at the
surface or inside a cell. Every cell in an animal
or a plant is surrounded by a membrane, referred
to as the cell surface membrane or plasma
membrane. Cell cytoplasm also contains
membranes, and organelles are surrounded by membranes. Cell membranes are very thin and
consist mainly of a double layer of
phospholipid molecules in which there are
proteins.

Question 10

Mitochondrion, Mitochondria, Mitochondrial

Answer 10

An organelle found in plant and animal cells. It
is the site of the biochemical reactions involved
in aerobic respiration. Although mitochondria
vary in size and shape, they usually appear as
small, elongated structures about a micrometre
in length. Each mitochondrion is surrounded by
a double membrane, the inner one of which is
folded to form cristae.

Question 11

Nuclear envelope

Answer 11

A layer which surrounds the
nucleus of a cell. It is called an envelope
because it is really composed of two membranes
perforated by tiny pores. mRNA leaves the
nucleus through these nuclear pores during the
process of protein synthesis.

Question 12

Nucleolus, Nucleoli

Answer 12

A dark staining body found
in the nucleus of a cell. The nucleolus is
involved in making ribosomes.

Question 13

Nucleus, Nuclei, Nuclear

Answer 13

A large organelle that
contains a cell’s genetic material. It is enclosed
by a nuclear envelope. This is composed of a
double membrane perforated by tiny pores. The
nucleus contains DNA, which is packaged into
chromosomes. This DNA contains genes, which
code for the proteins made by the cell.

Question 14

Chromatin

Answer 14

The DNA in the nucleus of the cell
when the cell is in interphase. At this stage in
the cell cycle, chromosomes are not visible. The
DNA in the nucleus is much more spread out. In
this condition it is known as chromatin.

Question 15

Rough endoplasmic reticulum, Rough ER

Answer 15

A
network of interconnected sacs in the cytoplasm
of a cell. These sacs are surrounded by
membranes. There are ribosomes attached to the
outer surfaces of the membranes. Proteins made
by the ribosomes are transported through the
endoplasmic reticulum to other parts of the cell.

Question 16

Middle lamella

Answer 16

The middle lamella is a pectin layer which cements the cell walls of two adjoining plant cells together. It is the first formed layer which is deposited at the time of cytokinesis. The cell plate that is formed during cell division itself develops into middle lamella or lamellum.

Question 17

Pit

Answer 17

A region where a plant cell wall is very thin
because only the first layer of cellulose has been
laid down. Pits help substances to move between
neighbouring plant cells.

Question 18

Plasmodesmata, Plasmodesma

Answer 18

Small fluidfilled
channels through the cell walls of plant
cells. Plasmodesmata allow dissolved molecules
such as mineral ions to pass directly from the
cytoplasm of one cell to the cytoplasm of the
next. These molecules do not have to pass
through cell membranes or cell walls.

Question 19

Parenchyma

Answer 19

Relatively unspecialised tissue
found in plants. Parenchyma cells have thin
cellulose cell walls and living contents. These
cells are very important in providing support in
young stems; they can photosynthesise and they
can store substances such as starch.

Question 20

Cellulose

Answer 20

A polysaccharide which is an
important component of plant cell walls. A
molecule of cellulose consists of a long straight
chain of beta-glucose molecules joined by
glycosidic bonds. Hydrogen bonds form
between neighbouring chains. These bonds hold
the cellulose molecules together in bundles
called microfibrils.

Question 21

Microfibril

Answer 21

Cellulose is a polymer made up of
long chains of beta-glucose molecules. In a plant
cell wall, these cellulose molecules are arranged
in bundles called microfibrils. The arrangement of the microfibrils makes the wall of the cell
very strong and helps it to resist the forces acting
on it.

Question 22

Hemicellulose, Hemicelluloses Polysaccharides

Answer 22

that have molecules made up of short chains of
various sugars. They are important in plant cell
walls where they help to bind cellulose
microfibrils together.

Question 23

Pectin, Pectate

Answer 23

A structural carbohydrate found
in plant cell walls. Pectin consists of a mixture
of polysaccharides, depending on its source.
The majority of the structure is formed of
repeating units of galacturonic acid. Pectins
combine with calcium ions to form calcium
pectates. Calcium pectates are found in and
between plant cell walls where they help to
cement cellulose fibres together.

Question 24

Epidermis, Epidermal

Answer 24

The outer layer of cells in
a multicellular organism. In plants, the epidermis is a single layer of cells surrounding
the other tissues in the roots, stems and leaves.
In mammals, it is the layer of dead cells which
lies above the living cells of the dermis in the
skin.

Question 25

Vascular tissue

Answer 25

One of the three main types of
tissue found in a plant. Vascular tissue consists
of xylem and phloem. Xylem transports water
and mineral ions from the roots, up through the
stem to the leaves. Phloem transports the
products of photosynthesis from the leaves to
other parts of the plant.

Question 26

Vascular bundle

Answer 26

In the stems and leaves of
young plants, particularly those which are not
woody, the vascular tissue is found in bundles.
These vascular bundles contain xylem vessels,
which transport water and mineral ions up the
stem to the leaves, and phloem tubes. The
phloem tubes transport the products of
photosynthesis.

Question 27

Dicotyledon, Dicot

Answer 27

A member of the group of
flowering plants which have two cotyledons in
their seeds. Dicotyledons include plants such as
buttercups, roses and oak trees. All dicotyledons
have seeds in which the embryo has two
cotyledons; flower parts such as petals arranged
in fours or fives; and leaves with veins which
spread out in a net-like arrangement.

Question 28

Xylem, Vessel

Answer 28

Xylem is a plant tissue whose
main function is to transport water and mineral
ions from the roots, up through the stem to the
leaves. It consists of a system of vessels. The
walls of these vessels contain lignin. Lignin
makes the walls stronger and more able to resist
the forces on them. Xylem provides a mass flow
system for transport of water and mineral ions.

Question 29

Phloem, Phloem sieve tubes, Sieve tube elements,

Sieve plates

Answer 29

A plant tissue that transports the
products of photosynthesis. It consists of a
system of tubes which takes these molecules
from the leaves to other areas of the plant such
as the developing flowers and fruits and the
roots. Phloem provides a mass flow system for
transport of the products of photosynthesis. Each tube is formed from a column of cells, sieve tube
elements, with perforated end walls, sieve plates,
to form a continuous tube.

Question 30

Sclerenchyma fibres

Answer 30

Long, thin plant cells
which are tapered at both ends. Sclerenchyma
fibres help to provide plants with support. They
have cell walls which are thickened with lignin.
They do not have living contents.

Question 31

Autolysis

Answer 31

Self-destruction of cells. The
breakdown of the tissues of an organism which
occurs after its death. It is caused by the action
of enzymes from the gut and from the
lysosomes. These enzymes bring about
decomposition by breaking down the organism’s
own cells. Autolysis also occurs during normal
development of organisms, for example fingers
are separated by autolysis of the tissue between
adjacent fingers.

Question 32

Diffusion gradient

Answer 32

Diffusion involves the
movement of a substance from where it is in a
high concentration to where it is in a lower
concentration. The difference in concentration
which allows diffusion to take place is
sometimes referred to as a diffusion gradient.
Oxygen diffuses into a cell down a diffusion
gradient.

Question 33

Transpiration, Transpire, Transpiration stream

Answer 33

Evaporation of water from the leaves of plants.
During transpiration, water evaporates from the
surfaces of the cells lining the substomatal
cavities and diffuses out through the stomata.
Water is drawn up the xylem according to the
cohesion-tension theory to replace the water lost
by evaporation.

Question 34

Stoma, Stomata, Stomatal

Answer 34

A small hole or pore
in the surface of a leaf through which gas
exchange takes place. Water is also lost through
the stomata during the process of transpiration.
Stomata are surrounded by guard cells which are
able to change the size of the stomatal pore.

Question 35

Substomatal cavity

Answer 35

Stomata are small holes or
pores in the surface of a leaf through which gas
exchange takes place. Immediately underneath
each stoma is a cell-lined space. This is the substomatal cavity. During transpiration, water
evaporates from the surfaces of the cells lining
this cavity and diffuses out through the stomata.

Question 36

Cohesion-tension

Answer 36

A theory explaining the
movement of water through the xylem of a plant
from the roots to the leaves. Water molecules
stick to each other by cohesion. As a result,
transpiration pulls a continuous, unbroken
water column up through the xylem. This water
column is under tension as a result of being
pulled up by transpiration and down by gravity.

Question 37

Cohesion

Answer 37

A force resulting from attraction
between molecules of the same substance. Water
molecules stick to each other by cohesion. As a
result, transpiration pulls a continuous,
unbroken water column up through the xylem in
a plant stem.

Question 38

Adhesion

Answer 38

A force resulting from attraction
between molecules of different substances. In
xylem, water molecules adhere to the molecules
of lignin and to other substances which make up
the walls of the vessel.

Question 39

Mass flow

Answer 39

Movement down a concentration
gradient of a liquid or gas and all the particles it
contains, for example, blood in the circulatory
system.

Question 40

Mass transport system

Answer 40

A system that transports
substances in bulk from one part of an organism
to another. Large organisms cannot rely on
diffusion alone to meet their needs. It is too
slow. They need mass flow to move substances
rapidly over long distances. Examples of mass
transport systems are the xylem in a flowering
plant and the blood system in an animal.

Question 41

Hydrostatic pressure

Answer 41

The pressure exerted by a
liquid. In the blood system, hydrostatic pressure
forces fluid out through the capillary walls. This
is very important in the formation of tissue
fluid. A reduction in hydrostatic pressure
brought about by water evaporating from the
leaves is important in moving water up through
the xylem of a plant.

Question 42

Companion cell

Answer 42

These long thin cells lie
alongside phloem sieve tubes and perform the
metabolic functions to maintain the sieve tube
cells which lack cell organelles and only have a
thin layer of cytoplasm around the edge of the
cell.

Question 43

Translocation

Answer 43

The transport of substances from
one part of a plant to another. Organic
molecules, such as sucrose, are transported
through the phloem. This mass transport
system relies on mass flow due to a pressure
difference between the two ends of the phloem
sieve tube.

Question 44

Turgid, Turgidity

Answer 44

A plant cell is described as
being turgid when the cell contents press against
the cell wall. If a plant cell is surrounded by a
solution with a high concentration of water
molecules, water will move into the cell by osmosis. As a result, the volume of the cell
contents will increase and press against the cell
wall.

Question 45

Binary fission

Answer 45

Bacteria reproduce asexually; the circular DNA replicates and the new cell content is synthesised before new cell wall forms to divide the cell into two roughly equal halves

Question 46

Double-blind test

Answer 46

A way of conducting a clinical
trial on, for example, a new drug. Neither the
patient nor the researcher conducting the trial
knows who is having the drug and who is being
treated with an inactive substance (placebo).
This helps to make the results of the trial
reliable.

Question 47

Placebo

Answer 47

When trials are carried out on new
drugs, it is usual to divide the participants into
two groups. Those in the experimental group are
given the drug. A second group forms the
control group. In some trials the control group
are given a placebo, which contains an inactive
dummy compound, indistinguishable in
appearance from the drug.

Question 48

Cotyledon, Cotyledons

Answer 48

A leaf from an embryo
plant inside a seed. In some plants, when seeds
germinate, the cotyledons may stay below the
surface of the soil and supply the developing
plant with nutrients. In others, the cotyledons
emerge from the soil, turn green and
photosynthesise. The number of cotyledons
present is one of the features used in classifying
plants. Monocotyledons have one cotyledon and
dicotyledons have two.

Question 49

Plumule

Answer 49

A young plant shoot. If the seed of a
dicotyledon plant such as a bean is cut open, an
embryo can be seen. A bean embryo has two
cotyledons which act as a food store, a radicle
or young root, and a plumule or young shoot.

Question 50

Radicle

Answer 50

A young plant root. If the seed of a plant
such as a bean is cut open, an embryo can be
seen. This embryo has two cotyledons which act
as a food store, a plumule or young shoot, and a
radicle or young root.

Question 51

Testa

Answer 51

A seed coat. In flowering plants, a seed
contains an embryo and a store of food material.
A protective coat called the testa surrounds the
embryo and its food store.

Question 52

Endosperm

Answer 52

During fertilisation in a flowering
plant, one of the male gametes fuses with two of
the nuclei in the embryo sac. The resulting
nucleus has three sets of chromosomes. It
divides rapidly and gives rise to the endosperm,
a mass of large cells that acts as a food store for
the developing embryo in the seed.

Question 53

Embryo sac

Answer 53

Part of the ovary of a flowering
plant. The embryo sac contains a number of
nuclei. One of these is the egg nucleus,
sometimes called the egg cell. This fuses with a
male gamete to form a zygote. The embryo sac
also contains two polar nuclei. The polar nuclei
fuse with a second male gamete to form a
nucleus with three sets of chromosomes. This
eventually develops into the endosperm which
provides food for the developing embryo. The
embryo sac is also called the ovule.