Unit 2: Multicellular Organisms Flashcards
Cell division (mitosis) is needed for:
Growth and repair
Why must cell division produce identical cells?
So that the new cells have the correct chromosome complement
Diploid cells
Diploid cells have two matching sets of chromosomes
Chromosomes
X shaped structures found in the nucleus of cells that carry genetic information (genes)
Chromosome structure
Two chromatids held together by a centromere
Mitosis
A type of cell division
Cell division stages:
-Chromosomes are not visible because they are uncoiled
-Chromosomes replicate to prepare for division
-Chromosomes coil up and become visible
-Nuclear membrane disappears, chromosomes line up on the equator
-Spindle fibres attach to the chromosomes
-Spindle fibres contract, chromatids are pulled apart and move to opposite poles of the cell
-The chromatids are now called chromosomes, nuclear membrane forms around each group of chromosomes
-Cytoplasm splits
-Two identical cells
Disease caused by uncontrolled cell division
Cancer
Stem cells
Unspecialised cells which can divide in order to self-renew, and have the potential to become different types of cells
Uses of stem cells
Required for growth and repair of animal tissues
Can be used in leukaemia treatment and skin grafts for burns
Types of stem cells
Embryonic— extracted from early stage embryos
Tissue— found throughout the body from birth to adulthood
Why is the use of embryonic stem cells controversial?
Because it involves the destruction of embryos
Cells show specialisation— what does this mean?
They have a special shape or structure which allows them to carry out a specific function
Example of a specialised cell
Sperm cells have tails which allow them to swim to an egg cell
Root hair cells have a large surface area to help them absorb water
Tissue
A group of specialised cells that work together to perform a particular function
Organ
A group of tissues working together to perform a specific function
Organ system
A group of organs working together
Hierarchy of cells to organ systems
Cells — tissues — organs — organ systems — organisms
Nervous system
The central nervous system (CNS) and other nerves
Central nervous system (CNS)
Brain and spinal cord
Parts of the brain
Cerebrum, cerebellum, medulla
Cerebrum
Controls conscious thought and voluntary decisions
Cerebellum
Controls balance and coordination
Medulla
Controls heart rate and breathing rate
Stimulus
A change in conditions
Receptors
Receptors detect sensory stimuli
Types of neurons
Sensory neurons, inter neurons, motor neurons
Neurons
Carry messages in the form of electrical impulses
Sensory neurons
Pass information from receptors to the CNS
Inter neurons
Operate / process information within the CNS
Motor neurons
Enable a response to occur at an effector (muscle or gland)
Electrical impulses
Electrical impulses carry messages along neurons
Chemicals in neurons
Chemicals transfer messages between neurons at synapses (they diffuse across)
Reflex actions
Fast, automatic responses
Example of a reflex action
If your hand touches something hot, a message is passed along a sensory neuron, across an inter neuron and along a motor neuron, which causes your muscle to contract
Reflex arc
A pathway of neurons
Hormones
Chemical messengers
Where are hormones released from?
Endocrine glands, into the bloodstream
Target tissue
The tissue a hormone has its effect on
Hormone specificity
Target tissues have cells in their membranes with complementary receptors for specific hormones, so only that tissue will be affected by the hormone
Examples of hormones
Insulin, human growth hormone
Blood glucose and hormones
Hormones are involved in controlling blood glucose levels
Hormones involved in controlling blood glucose levels
Insulin and glucagon
Where are insulin and glucagon produced?
In the pancreas
Insulin
Released when blood glucose levels are high. Activates enzymes in the liver which turn glucose into glycogen, lowering blood glucose level
Glucagon
Released when blood glucose levels are high. Activates enzymes in the liver which turn glycogen into glucose, raising blood glucose level
Gametes in plants
Male gamete: pollen, produced by anthers
Female gamete: ovules, produced by ovaries
The chromosome complement of gametes is
Haploid
Pollination
The pollen in a flower is transferred from the anthers to the stigma of the same / another flower
Fertilisation
The fusion of the nuclei of two haploid gametes to produce a diploid zygote
Haploid
One set of chromosomes
Gametes in animals
Female: Egg, produced by ovaries
Male: Sperm, produced by testes
Gametes
Sex cells
Features of an egg cell
Large food store– allows it to divide and grow after fertilisation
Features of a sperm cell
Has a tail so it can swim to the egg cell
Fertilisation in animals
The nucleus of the sperm cell fuses with the nucleus of the egg cell to produce a diploid zygote
Variation
The differences between members of the same species
Combining genes from two parents contributes to…
Variation
Continuous variation
Variation with a range of values (e.g. height)
Discrete variation
Variation with distinct values (e.g. blood type)
Polygenic traits
Characteristics controlled by more than one gene
Single gene traits
Characteristics controlled by one gene
Continuous variation is controlled by…
More than one gene (polygenic)
Discrete variation is controlled by…
One gene
Genes contain
Instructions to make proteins
Alleles
Different forms of a gene
Dominant alleles
Dominant alleles always show up in the appearance of an organism even if there is only one copy present in the gene pair. Dominant genes are represented with capital letters
Recessive alleles
Recessive alleles only show up in the appearance of an organism if they are paired with another recessive allele. Recessive genes are represented with lowercase letters
Phenotype
Describes the appearance of an organism
Genotype
Tells us which forms of the gene (which alleles) are present
Homozygous
Alleles are the same (e.g. RR or rr)
Heterozygous
Alleles are different (e.g. Rr)
P
Parental generation
F1
First generation (offspring of the parental generation)
F2
Second generation (offspring of the first generation)
Monohybrid cross
Used to track the inheritance of a gene through several generations
Why do plants need water?
Plants need water to carry out photosynthesis (water is a raw material of photosynthesis)
Water helps to keep plants upright
Water is important for transporting other materials such as minerals around the plant
How does water enter the plant?
Water enters the root hair cells via osmosis, the water is then transported in dead xylem vessels
Xylem vessels
Dead, hollow tubes that transport water in an upwards direction only
They are responsible for transporting water and minerals from the roots to the leaves
Lignin
A tough, woody substance
Xylem cells are lignified to withstand the pressure changes as water moves through the plant
Other functions of xylem
Made up of strong lignified tubes that help to support the plant
Mineral elements are absorbed from the soil and dissolved in water so they are transported by xylem
Stomata
Tiny pores which allow gas exchange and also allow water to leave the plant
Guard cells
Control the opening and closing of the stomata
Palisade mesophyll
Site of photosynthesis
Spongy mesophyll
Site of photosynthesis
Upper epidermis
Protects the leaf (creates a waxy cuticle to protect the leaf)
Lower epidermis
Protects the leaf
Leaf vein
Transports water and sugar around the leaf
Transpiration
The process of water moving through a plant and its evaporation through the stomata
When water reaches the xylem in the leaves, it continues to travel by…
Osmosis
Water moves through the leaf by…
Diffusion between the leaf cell walls
How is water used when it reaches the leaves?
Some water is used to carry out photosynthesis
Some water, however, is not used, and this water evaporates out of the leaf through the stomata
Factors that increase the rate of transpiration
Increasing temperature, increasing wind speed, increasing surface area, decreasing humidity
Every cell needs sugar to…
Release energy
Phloem
Living tissue that is involved in transporting sugar up and down the plant
In particular, sugar is transported to growing points which require a lot of food
Sieve plates
Found in phloem tubes, allow sugar to pass from one cell to the next
Companion cells
Controls sieve plates in phloem tubes
Importance of blood
Blood allows substances to be transported from one place to another
Role of oxygen in the body
Required to release energy from food
Where is oxygen carried from and to in the body?
From the lungs to all cells in the rest of the body
Carbon dioxide in the body
Waste product of respiration
Where is carbon dioxide carried from and to in the body?
From cells in the body to the lungs
Role of nutrients (e.g. glucose) in the body
Required to produce energy
Where are nutrients (e.g. glucose) carried from and to in the body?
From the small intestine to all cells in the rest of the body
What makes up blood?
Red blood cells, white blood cells, plasma
White blood cells
Part of the body’s immune system
Red blood cells
Involved in the transport of oxygen and carbon dioxide
Plasma
Pale yellow liquid part of blood, substances such as glucose and carbon dioxide dissolve in plasma and are carried around the body
What substance do red blood cells contain?
Haemoglobin
Role of haemoglobin
Picks up oxygen in the lungs; when oxygen binds to haemoglobin, a complex called oxy-haemoglobin in formed
Oxygen is released from oxy-haemoglobin in the tissues to be used for respiration
How are red blood cells specialised?
Biconcave shape increased their surface area and allows them to absorb oxygen quickly
They do not have a nucleus, this means that the cell has more room to contain haemoglobin
Pathogens
Disease-causing microorganisms (bacteria, viruses, fungi)
Two main types of white blood cell
Phagocytes, lymphocytes
Role of phagocytes
Carry out phagocytosis (engulf pathogens and digest them)
Role of lymphocytes
Produce proteins called antibodies which destroy pathogens
Antibody specificity
Each antibody is specific to a particular pathogen, different antibodies have different shaped receptor sites
The shape of the receptor site on an antibody is complementary to the shape of molecules on the surface of the particular pathogen
Stages of phagocytosis
Phagocyte engulfs pathogen
Pathogen ingested by powerful enzyme
Harmless pathogen pieces are released from the phagocyte
Types of blood vessels
Veins, arteries, capillaries
Arteries
Carry blood away from the heart
Thick, muscular walls to withstand high pressure
Narrow central channel
When the heart pumps blood into the artery, the pressure causes the walls to expand— this is what you feel as your pulse
Veins
Carry blood back to the heart
Thinner walls and wider central channel than arteries
The blood in veins is much lower pressure than the blood in arteries
Contain structures called valves which prevent the backflow of blood (blood can only flow in one direction through a valve)
Capillaries
Form networks at tissues and organs
Allow substances to be exchanged from the blood and the tissues
Thin walls to ensure that diffusion happens quickly
Some capillaries may have walls that are only one cell thick
Large surface area also allows diffusion to happen quickly
Muscle that makes up the heart
Cardiac muscle
Chambers in the heart
Upper chambers: right atrium, left atrium
Lower chambers: right ventricle, left ventricle
Vena cava
Carries deoxygenated blood from the body to the heart
Why do the ventricles have thicker walls than the atria?
Because they have to push blood much further
Pulmonary artery
Carried deoxygenated blood from the heart to the lungs
Pulmonary vein
Carries oxygenated blood from the lungs to the heart
Aorta
Carries oxygenated blood from the heart to the rest of the body
Tissues contain capillary networks to…
Allow the exchange of materials at cellular level
Oxygen and nutrients must be…
Absorbed into the bloodstream to be delivered to cells for respiration
Waste materials such as carbon dioxide must be…
Removed from cells into the bloodstream
Features of surfaces involved in the absorption of materials
Large surface area
Thin walls
Extensive blood supply
These increase the efficiency of absorption
Capillaries allow the body cells to…
Receive oxygen and remove carbon dioxide
Lungs
Gas exchange organs
Allow oxygen to enter the blood and carbon dioxide to be removed from the blood
This process is known as gas exchange and takes place in the alveoli
Alveoli
Tiny air sacs surrounded by many blood capillaries
Oxygen diffuses from the alveoli to the blood
Carbon dioxide diffuses from the blood to the alveoli
The digestive system is also known as
The alimentary canal
Two main purposes of the digestive system
Digestion (the breakdown of food particles)
Absorption of the nutrients from food
The small intestine
The location where nutrients from food are absorbed
Villi
(Singular is villus)
Small, finger-like projections found in the small intestine that allow it to absorb nutrients from food efficiently
Blood capillaries absorb
Glucose and amino acids
Lacteals absorb
Fatty acids and glycerol
