tissues and organs

Question 1

building block sequence

Answer 1

cell> tissue> organ> organ system> organism

Question 2

tissue

Answer 2

Tissues- are composed of groups of
specialised cells that carry out the same (or
very small number of) functions.
• E.g palisade layer in a plant leaf contains
palisade cells; cells that are all very similar in
shape and all adapted to carry out the same
function (photosynthesis).

Question 3

organ

Answer 3

Organ– composed of tissues grouped
together that carries out one or more
functions
• e.g a leaf (has palisade tissue, vascular tissue,
epidermal and spongy mesophyll tissu

Question 4

the ileum

Answer 4

This ileum is an example of an organ in
humans
• Its primary role is the absorption of digested food
and moving undigested food through to the colon
• The ileum contains a range of tissues (e.g epithelial
tissue that form boundary between ileum and lumen
of the gut, muscle and blood tissue.

Question 5

layers of the ileum

Answer 5

The intestinal wall is made up of four distinct
layers
• Mucosa
• Muscularis Mucosa
• Submucosa
• Muscularis externae
• Serosa → outermost

Question 6

mucosa

Answer 6

This layer that is in contact with the food in the
gut lumen. The surface area of the mucosa is
increased by the presence of villi
• **Each villus are made up of columnar
epithelial cells, which absorb food molecules
• The further surface area of these cells are
increased by the presence of microvilli *

Question 7

muscularis mucosa

Answer 7

This is a thin layer of muscle that lies between the
submucosa and the mucosa.
It helps movement of the villi and increases contact with the digested food

It is able to do this as small strands of muscle extend from
the main muscularis mucosa layer up through the mucosa
into each villus, with contraction of these strands help to
produce the characteristic ‘wafting ‘movement of the villi

Question 8

sub mucosa

Answer 8

This layer contains connective tissue, blood and
lymphatic vessels. Connective tissue provides
support.
• The blood and lymph carry absorbed food
products away from the intestine to the liver via
the hepatic portal vein

Question 9

muscularis externa

Answer 9

It is made up of outer
longitudinal muscle fibres
(muscle that runs along the
length of the alimentary
canal).
• inner circular muscle fibres
(muscle that runs around
the alimentary canal)

Question 10

peristalsis

Answer 10

this allows gut to perform:

• Contraction of longitudinal muscle : cause
perpendicular movements
• Contraction of circular muscle : cause local
constrictions – actions aids to churn and mix
food
• Contracion of circular muscle help push food along gut in peristaltic waves

Question 11

serosa

Answer 11

This is the outermost protective layer of the
alimentary canal.
• It also plays a role in supporting the
alimentary canal as it is connected to the
mesentery, which in turn is connected to the
peritoneum of the abdominal cavity.

Question 12

microvilli

Answer 12

The columnar epithelial cells have their
surface area extended by the presence of
numerous microvilli that give a brush border
appearance
• The is a rich supply of mitochondria to make
*ATP for active transport

Question 13

absorption in the illeum

Answer 13

The products of digestion mostly:
• Monosaccharide sugars
• Amino acids
• Fatty acids and glycerol

Question 14

absorption occurs by

Answer 14

diffusion
active transport
pinocytosis

Question 15

goblet cells

Answer 15

• goblet cells are found within the columnar
epithelium cells) for the secretion of mucus.

Question 16

mucus

Answer 16

Mucus provides a slimy PROTECTIVE layer to
lubricate the lining of the alimentary canal for
the movement of material through the
intestines. (protect the epithelial cells from self
digestion by the digestive enzymes)

Question 17

crypt of lieberkuhn

Answer 17

The cells at the bottom of the crypts are
continually dividing by mitosis to produce new
cells that continually move up the surface of
the villi, like a conveyer belt, as a new cells are
produced below them. When they reach the
tip of the villus they are replaced

Question 18

paneth cells

Answer 18

Paneth cells at the base of the crypts, have an
anti-microbial function in protecting their
neighbouring actively dividing cell. Other cells
lining the crypts are involved in mucus secretion

Question 19

mesophytic leaf

Answer 19

• The mesophytic leaf is a classic example of
such as case as it displays ideal properties for
the process:
• A large flat surface area with chlorophyll concentrated in the
upper layers of cells next to the incident light for maximum
light absorption
• Thin profile – most light is absorbed in the first mm or so of
tissue. This also ensures that diffusing gases only have short
distances to move.
• The presence of stomata (leaf pores) through which gases can
diffuse easily into a network of air spaces (spongy mesophyll)
• The presence of vessels to transport water to the cells and
others to transport the products of photosynthesis to the non
photosynthetic parts

Question 20

upper epidermis

Answer 20

Most cells of the epidermis have no chloroplasts –
and therefore cannot photosynthesise. The role of
this layer is to reduce water loss from the leaf.

• One function of the upper epidermal cells is to
secrete the protective waxy material that results in
the formation of the waxy cuticle. This greatly
reduces evaporative water loss and also serves to
protect the entry of pathogens

Question 21

palisade mesophyll

Answer 21

The Primary photosynthesing region in the leaf
• the palisade mesophyll layer is immediately
beneath the upper epidermis and are highly
adapted for the absorption of light and hence the
carrying out photosynthesis

Question 22

arrangement of palisade mesophyll

Answer 22

• The palisade cells are arranged regularly in order to
pack in as many as possible
• These tall columnar vertically orientated cells are
packed close together and have cytoplasm densely
packed with chloroplasts to maximise
photosynthesis

Question 23

spongy mesophyll

Answer 23

• Immediately below the palisade layer.
• This group of cells is adapted to allow efficient
gas exchange within the leaf.
• They are more loosely and irregularly
arranged (which gives a large gaseous
exchange surface) with numerous intercellular
airspaces allow gases to diffuse to and from
cells .
• Since leaves are thin gases only have a short
distance to move.
• Although responsible for some photosynthesis
numbers of chloroplasts are lower when
compared to the palisade cells.

Question 24

Transport Vessels: Xylem and
Phloem

Answer 24

• Within the spongy mesophyll layer is the leaf
vascular tissue (can be found in leaf veins).
• These tissues are responsible for the
transport of materials into and out of the leaf.
• The vascular tissue forms a continuous
network running from the root to all other
parts of the plant via the stem.

Question 25

lower epidermis

Answer 25

This layer resembles the upper epidermis but
with 2 important differences:
•
• The waxy cuticle is a lot thinner, compared to
the upper epidermis, if present at all as less
transpiration tends to occur through the lower
epidermis.
• The density of stomata is much higher

Question 26

guard cells and stomata

Answer 26

Stomata are the pores created between 2 guard cells. Stomata are
often considered as a necessary evil: they are important to allow gas
exchange but also allow a great deal of water to evaporate from the
leaf.
• To overcome this problem stomata can be opened and closed
through changes that occur in the guard cells.
• Guard cells contain chloroplasts
stomata remain open in favour of photosynthesis